Rewritable optical recording medium and optical recording method

ABSTRACT

A rewritable optical recording medium includes a substrate and a phase-change type recording layer. A portion in a crystalline state corresponds to an unrecorded or erased state, and a portion in an amorphous state correspond to a recorded state, to record EFM modulated information by forming amorphous marks by irradiating the recording layer with a recording laser beam, and the recording is carried out by irradiating a recording laser beam having a wavelength of about 780 nm through an optical system having a numerical aperture NA of 0.5 or 0.55, at 24-times velocity or 32-times velocity of the reference velocity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of PCT/JP03/0 1509, filedon Feb. 13, 2003, which was not published under PCT Article 21(2) inEnglish and claims the benefit of priority under 35 U.S.C. §120 fromU.S. Ser. No. 10/890,414, filed Jul. 14, 2004, and claims the benefit ofpriority under 35 U.S.C. §119 from Japanese Patent Application Nos.2002-034827, filed Feb. 13, 2002; 2002-074818, filed Mar. 18, 2002;2002-126491, filed Apr. 26, 2002; 2002-317858, filed Oct. 31, 2002; and2002-344557, filed Nov. 27, 2002 the entire contents of each applicationare incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a rewritable optical recording medium(in the present invention, a rewritable optical recording medium maysimply be referred to as an optical recording medium, a medium, anoptical disk or a disk) which has retrieving interchangeability with areadout-only medium specified in conventional CD-ROM or DVD (-ROM)standards, and a recording method therefor. Particularly, it provides arewritable optical recording medium capable of one-beam overwriting at alinear velocity as high as at least 20 m/s. Further, it provides arecording method, whereby excellent recording can be carried out withina wide range of recording linear velocity.

BACKGROUND ART

With a compact disk (CD) or a digital versatile disk (DVD), it is commonthat recording of binary signals and detection of tracking signals arecarried out by utilizing a change in reflectivity caused by interferenceor reflected lights from the mirror surface and the bottom of pits.

In recent years, phase-change type rewritable compact disks (CD-RW,CD-Rewritable) or phase-change type rewritable DVD (tradename: DVD-RW,DVD+RW, in this specification, rewritable DVD may sometimes be referredto as RW-DVD) have been used as optical recording media interchangeablewith CD or DVD.

Such phase-change type CD-RW or RW-DVD utilizes a phase difference and adifference in reflectivity caused by a difference in the refractiveindex between an amorphous state and a crystalline state to detectrecording information signals. A usual phase-change type CD-RW or RW-DVDhas a structure comprising a substrate, and a lower protective layer, aphase-change type recording layer, an upper protective layer and areflective layer, formed on the substrate, so that multiple interferenceof these layers can be utilized to control the difference inreflectivity and the phase difference and to provide interchangeabilitywith CD or DVD. Further, recording on CD-RW or RW-DVD means recording byoverwriting wherein recording and erasing are carried outsimultaneously.

As a result, although it is difficult to secure interchangeabilitycovering a high reflectivity as high as at least 70%, it is possible tosecure interchangeability of recording signals and groove signals withina range where the reflectivity is lowered to a level of from 15 to 25%in the case of CD-RW or to a level of from 18 to 30% in the case ofRW-DVD, and retrieving can be carried out by a current CD drive or DVDdrive for retrieving only, if an amplifying system to complement the lowreflectivity is added to the retrieving system.

However, one of problems in using CD-RW or RW-DVD is that the recordingvelocity and the transfer rate are low. The reference velocity(hereinafter referred to also as 1-time velocity) inrecording/retrieving of CD is a linear velocity (in this specification,“a linear velocity” may simply be referred to as “linear speed” of from1.2 to 1.4 m/s. However, for CD-ROM, a high velocity retrieving at alevel of 40-times velocity at the maximum has been already realized, anda low velocity at a level of 1-time velocity is used only for retrievingof musics or images. Usually, in up to 16-times velocity retrieving, aconstant linear velocity mode (CLV) inherent to CD is used, but in 24 to40-times velocity retrieving, the transfer rate, access and seek timesfor the outer periphery data have been remarkably speeded up by anapplication of a constant angular velocity mode (CAV).

Speeding up in recording is in progress also for CD-RW, but in CLV mode,the speed is still at a level of 12-times velocity at best. Usually,with CD-RW, it takes a time as much as 74 minutes (or 63 minutes) ifrecording is made over the entire surface at 1-time velocity, and evenat 12-times velocity, it takes about 6 minutes. However, at 20-timesvelocity, recording can be completed in 5 minutes, whereby theapplication of CD-RW can be substantially broadened for recording dataof large amounts such as musics and images.

Further, as a peripheral memory device for a computer, CD-R has alreadyaccomplished 24-times velocity for recording, and also for CD-RW, it isdesired to increase the transfer rate in recording.

On the other hand, the reference velocity (hereinafter referred to alsoas 1-time velocity) in retrieving of DVD is a linear velocity of 3.49m/s, but with DVD-ROM, high velocity retrieving at a level of 16-timesvelocity at the maximum has already been realized, and a low velocity ata level of 1-time velocity is used only for retrieving of musics orimages.

Speeding up in recording is in progress also for RW-DVD, but in CLVmode, it is still at a level of 2.4-times velocity at best. Usually,with RW-DVD, it takes a time as much as about 60 minutes if recording iscarried out over the entire surface at 1-time velocity, and even at2.4-times velocity, it takes about 25 minutes. However, at 6-timesvelocity, recording can be completed in 10 minutes, and application ofRW-DVD can be substantially broadened for recording data of largeamounts such as musics or images.

Therefore, a phase-change medium and a recording method have beendesired whereby recording can be carried out at a higher velocity.

However, a rewritable phase-change medium capable of recording up to ahigh linear velocity of at least 20-times velocity for CD or at least6-times velocity for RW-DVD, has not yet been realized. This means thata rewritable CD or DVD medium which is overwritable at a high linearvelocity at a level of exceeding a linear velocity of 20 m/s, has notyet been realized.

A first reason for why such a rewritable phase-change medium can not berealized, is that it is difficult to simultaneously satisfy the archivalstability of amorphous marks and erasing in a short time by high speedcrystallization of amorphous marks.

For example, with a recording material comprising a SbTe alloy as themain component which is used as a material for a recording layer ofCD-RW overwritable at 1 to 4-times velocity or RW-DVD overwritable at upto about 2.4-times velocity, high speed crystallization is possible byrelatively increasing the Sb content, whereby overwriting at a linearspeed of at least 20 m/s will be possible. However, according to a studymade by the present inventors, it has been found that such an increaseof the Sb content tends to substantially impair the archival stabilityof amorphous marks, whereby amorphous marks will disappear byrecrystallization to such an extent that no retrieving is possible,within 1 to 2 years at room temperature or in a few days in a hightemperature environment at a level of from 50 to 80° C. in the interiorof the recording apparatus. Otherwise, there is a serious problem suchthat amorphous marks start to disappear by repeated retrieving fromabout a few hundreds to a few thousands times by a laser beam of at most1 mW, and it has been found that the reliability as a recording mediumcan not be maintained.

In addition to the necessity to solve such a problem, CD-RW or RW-DVDhas a restriction such that it is necessary to secure retrievinginterchangeability with a widely used CD-ROM drive or DVD-ROM drive forretrieving only.

For example, in the case of CD-RW, in order to secure retrievinginterchangeability, it is necessary to satisfy not only a highmodulation at a level of a modulation of from 55 to 70% but also areflectivity of from 15 to 25% and other servo signal characteristics.On the other hand, in the case of RW-DVD, in order to secure retrievinginterchangeability, it is necessary to satisfy not only a highmodulation at a level of a modulation of from 55 to 70% but also areflectivity of from 18 to 30% and other servo signal characteristics.

Further, a second reason for why CD-RW or RW-DVD overwritable at a highlinear velocity of at least 24 m/s has not yet been realized, is that afairly strict recording pulse strategy (pulse division method) isspecified in CD-RW standards or RW-DVD standards.

Namely, in CD-RW standards Orange Book, Part 3, a recording pulsestrategy as shown in FIG. 1, is specified. Accordingly, in a currentlypractically used recording device, IC for generating such a recordingpulse strategy is employed. Accordingly, with a currently practicallyused recording device, it is obliged to carry out recording in a widerange of linear velocity ranging from 1-time velocity to 8- to 10-timesvelocity by such a recording pulse strategy or by a recording pulsestrategy having certain changes made thereto.

Also in standards for DVD-RW or DVD+RW as standards for rewritable DVD,a similar recording strategy is specified. A characteristic of such arecording strategy is that an amorphous mark having a nT mark length isdivided into n−1 recording pulses and cooling pulses (off-pulses) forrecording. Therefore, in such a recording strategy, an average repeatingperiod for a pair of a recording pulse and a cooling pulse is made to beabout 1T.

FIG. 1(a) shows EFM modulated data signals having time lengths of from3T to 11T, and FIG. 1(b) shows the practical recording laser powersgenerated on the basis of such data signals. Pw represents a writingpower to form an amorphous mark by melting and quenching the recordinglayer, Pe represents an erasing power to erase an amorphous mark bycrystallization, and usually, a bias power Pb is substantially the sameas a retrieving power Pr of a retrieving laser beam. Writing power (Pw)irradiation sections are referred to as recording pulses, and bias powerirradiation sections are referred to as off-pulses.

In the case of EFM+ modulation, data signals having time lengths of 14Tare added to the above-mentioned data signals having time lengths offrom 3 to 11T.

Here, in the above-mentioned recording strategies, a repeating periodfor a recording pulse and an off-pulse is basically constant as areference clock period T. The reference clock period T is made to have ahigh frequency in proportion to the linear velocity in high linearvelocity recording.

At a reference velocity of 1-time velocity for CD, T=231 nsec, but at24-times velocity, T=9.6 nsec, and at 32-times velocity, T=7.2 nsec.Accordingly, in a case where the recording pulse strategy shown in FIG.1 is used in high linear velocity recording at least 24-times velocity,the time widths of divided recording pulses and off-pulses in FIG. 1will be less than 5 nsec by the above-mentioned change for highfrequency corresponding to the high velocity recording.

On the other hand, at a reference velocity of 1-time velocity for DVD,T=38.2 nsec, but at 6-times velocity, T=6.4 nsec, and at 8-timesvelocity, T=4.8 nsec. Accordingly, in high linear velocity recording atleast 6-times velocity, the time widths of divided recording pulses andoff-pulses in FIG. 1 will be at most 3 nsec by the above-mentionedchange for high frequency corresponding to such high velocity recording.

Whereas, by irradiation with a laser beam having a usual writing power,it takes from 1 to 3 nsec in rising or falling. Accordingly, at such ahigh frequency, the rise time or the fall time can not be neglected, andthe lengths of recording pulse sections and the lengths of off-pulsesections will further substantially be shortened and will besubstantially less than 5 nsec (in the case of CD-RW) or less than 3nsec (in the case of RW-DVD). In such a case, heating for recordingpulses tends to be inadequate, and the required writing power will besharply high. On the other hand, cooling for the off-pulse sections alsotends to be inadequate, whereby a cooling rate required for the changeinto an amorphous state tends to be hardly obtainable. Further, for thehigh linear velocity recording, it is common to employ a material havinga high erasing speed i.e. a high crystallization speed for the recordinglayer for CD-RW or RW-DVD. Accordingly, deficiency in the cooling ratefor the above-mentioned off-pulse sections, tends to lead torecrystallization of the once-melted region.

Accordingly, with the recording pulse strategy shown in FIG. 1, it isvery difficult to carry out high velocity recording at a level of atleast 24-times velocity on CD-RW or to carry out high velocity recordingat a level of at least 6-times velocity on RW-DVD.

In order to solve such problems, some of the present inventors havealready realized overwriting on CD at 16-times velocity or on DVD at5-times velocity by a division method wherein the repeating period of arecording pulse and an off-pulse is set to be 2T base(JP-A-2001-331936). However, even if such a division method of 2T baseis employed, it is necessary, as mentioned above, to employ a materialhaving a high crystallization speed for high linear velocity recordingat a level of at least 24-times velocity for CD or at a level of atleast 6-times velocity for DVD, while, if such a material is employed,the recrystallization phenomenon will be more serious due to deficiencyof the cooling rate.

It is an object of the present invention to provide a rewritable opticalrecording medium to be used for high velocity recording at a level of atleast 20 m/s and a recording method therefor.

A specific object of the present invention is to provide CD-RW to beused for high velocity recording at a level of at least 24-timesvelocity and a recording method therefor. More specifically, the objectis to provide a rewritable medium having retrieving interchangeabilitywith CD with respect to the recording signal format and a recordingmethod therefor, wherein in CD-RW, an amorphous state of the recordinglayer corresponds to a recorded mark, and mark length recording iscarried out by EFM modulation (i.e. by a combination of mark lengths andspace lengths between marks, having time lengths of from 3T to 11T,based on the reference clock period T of data).

A specific object of the present invention is to provide a rewritableDVD recording medium to be used for high velocity recording at a levelof at least 6-times velocity. More specifically, the object is toprovide a rewritable medium having retrieving interchangeability withDVD with respect to the recording signal format, and a recording methodtherefor, wherein an amorphous state of the recording layer correspondsto a recorded mark, and mark length recording is carried out by EFM+modulation, i.e. a combination of mark lengths and space lengths betweenmarks, having time lengths of from 3T to 14T, based on the referenceclock period T of data.

DISCLOSURE OF THE INVENTION

In the first aspect, the present invention provides a rewritable opticalrecording medium comprising a substrate having a guide groove formedthereon, and a phase-change type recording layer, wherein a portion in acrystalline state of the phase-change type recording layer correspondsto an unrecorded or erased state, and a portion in an amorphous state ofthe phase-change type recording layer corresponds to a recorded state,so that an amorphous mark corresponding to the recorded state will beformed upon irradiation with a recording laser beam, and wherein whenEFM modulation signals are recorded by overwriting 10 times by onerecording method selected from the conditions of the following recordingmethods CD1-1 and CD1-2 while maintaining the reference clock period Tto satisfy VT=V₁T₁, where V₁ is a reference velocity (1-time velocity)which is set to be a linear velocity of 1.2 m/s, V is a linear velocitywhich is selected to be either V=24V₁ i.e. a linear velocity 24 timesthe reference velocity, or V=32V₁ i.e. a linear velocity 32 times thereference velocity, and T₁ is 231 nsec, and then, record signals areretrieved at 1-time velocity, the modulation m₁₁ of an eye pattern ofthe record signals obtained by the retrieving is from 60 to 80%, the topvalue R_(top) of the reflectivity of the eye pattern of the recordsignals is from 15 to 25%, and jitters of the respective mark lengthsand the respective spaces between marks are at most 35 nsec;

Recording Method CD1-1:

A laser beam having a wavelength of 780 nm is applied via an opticalsystem having a numerical aperture NA of 0.5, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.2 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁+Δ₁ (whereΔ₁=0.3 to 0.6), α_(i)′=αc (where i is an integer of from 2 to m−1),β_(i−1)′+α_(i)′=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.3 to 0.6, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 20 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁, β_(m−1),Δ_(m−1), α_(m) and Δ_(m) are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′, β₂ and β₂′ are made to be equal toα₁, α₁′, α₃, α₃′, β₃ and β₃′ in the case where m is 3, respectively, β₁is made to be equal to either β₁ or β₂ in the case where m is 3, and β₁′is made to be equal to either β₁′ or β₂′ in the case where m is 3, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out;

Recording Method CD1-2:

A laser beam having a wavelength of 780 nm is applied via an opticalsystem having a numerical aperture NA of 0.5, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α_(i)=0.7 to 1.4, α_(i)=0.7 to1.2 (where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.2 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁, α_(i)′=αc(where i is an integer of from 2 to m−1), β_(i−1)′+α_(i)′=2 (where i isan integer of from 3 to m−1), β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 0.6), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)≦0.6),Δ_(mm)=Δ_(m−1)+Δ_(m)=0.5 to 1.2, and β_(m)′=β_(m), a recording laserbeam having a constant writing power Pw sufficient to melt the recordinglayer (provided that Pw is from 20 to 40 mW, and Pe/Pw=0.2 to 0.6) isapplied within a time of α_(i)T and α_(i)′T (where i is an integer offrom 1 to m), and a recording laser beam having a bias power Pb of lessthan 1 mW is applied within a time of β_(i)T and β_(i)′T (where i is aninteger of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), β₁(=β₁′), αc, β_(m−1), Δ_(m−1), α_(m),β_(m) and Δ_(m)′ are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₁, β₂′, α_(3, α) ₃′, β₃ and β₃′ in the case where mis 3, respectively, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out.

In the second aspect, the present invention provides a rewritableoptical recording medium comprising a substrate having a guide grooveformed thereon, and a phase-change type recording layer, wherein aportion in a crystalline state of the phase-change type recording layercorresponds to an unrecorded or erased state, and a portion in anamorphous state of the phase-change type recording layer corresponds toa recorded state, so that an amorphous mark corresponding to therecorded state will be formed upon irradiation with a recording laserbeam, and wherein when EFM+ modulation signals are recorded byoverwriting 10 times by one recording method selected from theconditions of the following recording methods DVD1-1 and DVD1-2 whilemaintaining the reference clock period T to satisfy VT=V₁T₁, where V₁ isa reference velocity (1-time velocity) which is set to be a linearvelocity of 3.49 m/s, V is a linear velocity which is selected to be oneof V=6V₁ i.e. a linear velocity 6 times the reference velocity, V=8V₁i.e. a linear velocity 8 times the reference velocity, V=10V₁ i.e. alinear velocity 10 times the reference velocity and V=12V₁ i.e. a linearvelocity 12 times the reference velocity, and T₁ is 38.2 nsec, and then,record signals are retrieved at 1-time velocity, the modulation m₁₄ ofan eye pattern of the record signals obtained by the retrieving is from55 to 80%, the top value R_(top) of the reflectivity of the eye patternof the record signals is from 18 to 30%, and the clock jitter of theretrieved signals is at most 15%;

Recording Method DVD1-1:

A laser beam having a wavelength of 650 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.65, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11 and 14),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.2 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁+Δ₁ (whereΔ₁=0.3 to 0.6), α_(i)′=αc (where i is an integer of from 2 to m−1),β_(i−1)′-1′+α_(i)′=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.3 to 0.6, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 10 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁, β_(m−1),Δ_(m−1), α_(m) and Δ_(m) are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′, β₂ and β₂′ are made to be equal toα₁, α₁′, α₃, α₃′, β₃ and β₃′ in the case where m is 3, respectively, β₁is made to be equal to either β₁ or β₂ in the case where m is 3, and β₁′is made to be equal to either β₁′ or β₂′ in the case where m is 3, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section α₁′T is carried out;

Recording Method DVD1-2:

A laser beam having a wavelength of 650 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.65, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11 and 14),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.4 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁, α_(i)′=αc(where i is an integer of from 2 to m−1), β_(i−1)′+α_(i)′=2 (where i isan integer of from 3 to m−1), β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 0.6), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)≦0.6),Δ_(mm)=Δ_(m−1)+Δ_(m)=0.5 to 1.2, and β_(m)′=β_(m), a recording laserbeam having a constant writing power Pw sufficient to melt the recordinglayer (provided that Pw is from 10 to 40 mW, and Pe/Pw=0.2 to 0.6) isapplied within a time of α_(i)T and α_(i)′T (where i is an integer offrom 1 to m), and a recording laser beam having a bias power Pb of lessthan 1 mW is applied within a time of β_(i)T and β_(i)′T (where i is aninteger of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), β₁(=β₁′), αc, β_(m−1), Δ_(m−1), α_(m),β_(m) and Δ_(m)′ are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₂, β₂′, α_(3, α) ₃′, β₃ and β₃′ in the case where mis 3, respectively, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out.

In the third aspect, the present invention provides a recording methodfor a rewritable optical recording medium, which comprises recordinginformation on a rewritable optical recording medium by a plurality ofrecord mark lengths and space lengths between record marks, wherein:

between record marks, a laser beam having an erasing power Pe capable ofcrystallizing an amorphous phase is applied to form spaces betweenrecord marks, and

when the time length of one record mark is represented by nT (where T isthe reference clock period), for a record mark of n=2m (where m is aninteger of at least 1), of which the time length (n−j)T (where j is areal number of from −2.0 to 2.0) is divided into m sections of α_(i)Tand β_(i)T comprising α₁T, β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T(provided that Σ_(i)(α_(i)+β_(i))=n−j) and for a record mark of n=2m+1(where m is an integer of at least 1), of which the time length (n−k)T(where k is a real number of from −2.0 to 2.0) is divided into msections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . ., α_(m)′T and β_(m)′T (provided that Σ_(i)(α_(i)′+β_(i)′)=n−k), a laserbeam having a constant writing power Pw sufficient to melt the recordinglayer is applied within a time of α_(i)T and α_(i)′T (where i is aninteger of from 1 to m), and a laser beam having a bias power Pb isapplied within a time of β_(i)T and β_(i)′T (where i is an integer offrom 1 to m); and further,

when m≧3,

for a record mark of n=2m, when the start time for nT mark isrepresented by T₀,

(i) after a delay time T_(d1)T from T₀, α₁T is generated, then,

(ii) within i=2 to m, β_(i−1)T and α_(i)T are alternately generated inthis order, while β_(i−1)+α_(i) maintains about period 2 (provided thatat i=2 and/or i=m, β_(i−1)+α₁ may be deviated from about period 2 withina range of ±0.5, and when m≧4, β_(i−1) and α_(i) take constant values βcand αc, respectively, within i=3 to m−1), and then,

(iii) β_(m)T is generated, and

for a record mark of n=2m+1, when the start time for nT mark isrepresented by T₀,

(i) after a delay time T_(d1)′T from T₀, α₁′T is generated, then,

(ii) within i=2 to m, β_(i−1)′T and α_(i)′T are alternately generated inthis order, while β_(i−1)′+α_(i)′ maintains about period 2 (providedthat at i=2 and/or i=m, β_(i−1)′+α_(i)′ may be deviated from aboutperiod 2 within a range of ±2, and when m≧4, β_(i−1)′ and α_(i)′ takeconstant values βc and αc, respectively, within i=3 to m−1), and then,

(iii) β_(m)′T is generated, and

with the same m, for a record mark of n=2m and a record mark of n=2m+1,T_(d1)=T_(d1)′, α₁=α₁′, β₁=β₁′ and α_(m)≠α_(m)′, and at least one setselected from (β_(m−1) and β_(m−1)′) and (β_(m) and β_(m)′) takesdifferent values.

Further, in the present invention, the expression reading “□ is within arange of ◯ to Δ” means “◯≦□≦Δ”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is views illustrating an example of a conventional recordingpulse-dividing method.

FIG. 2 is schematic views of retrieving waveforms (eye patterns) of EFMmodulation signals.

FIG. 3 is a view illustrating a recording pulse-dividing method.

FIG. 4 is a view illustrating influences of the heat dissipation effectof the reflective layer, the composition of the recording layer and therecording method over the process for formation of an amorphous stateand recrystallization at various recording linear velocities.

FIG. 5 is a view illustrating an embodiment of the recordingpulse-dividing method in the recording method of the present invention.

FIG. 6 is a schematic view of a recording device to be used for therecording method of the present invention.

FIG. 7 presents data showing optical recording characteristics of anoptical recording medium having a GeSbTe type recording layer, when24-times velocity recording is carried out by a prescribed recordingmethod.

FIG. 8 presents data showing optical recording characteristics of anoptical recording medium having a GeSbTe type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 9 presents data showing optical recording characteristics of anoptical recording medium having a GeSbTe type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 10 presents data showing repeated overwriting characteristics of anoptical recording medium having a GeSbTe type recording layer, when24-times velocity recording is carried out by a prescribed recordingmethod.

FIG. 11 presents data showing repeated overwriting characteristics of anoptical recording medium having a GeSbTe type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 12 presents data showing repeated overwriting characteristics of anoptical recording medium having a GeSbTe type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 13 presents data showing optical recording characteristics of anoptical recording medium having a InGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 14 presents data showing optical recording characteristics of anoptical recording medium having a InGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 15 presents data showing optical recording characteristics of anoptical recording medium having a InGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 16 is a view illustrating a recording pulse-dividing method.

FIG. 17 shows a method for determining a recording pulse-dividingmethod.

FIG. 18 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 19 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 20 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 21 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 22 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 23 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 24 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 25 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 26 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when32-times velocity recording is carried out by another prescribedrecording method.

FIG. 27 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 28 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 29 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when32-times velocity recording is carried out by another prescribedrecording method.

FIG. 30 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 31 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 32 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when32-times velocity recording is carried out by another prescribedrecording method.

FIG. 33 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 34 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 35 presents data showing optical recording characteristics of anoptical recording medium having a SnGeSb type recording layer, when32-times velocity recording is carried out by another prescribedrecording method.

FIG. 36 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when24-times velocity recording is carried out by another prescribedrecording method.

FIG. 37 presents data showing repeated overwriting characteristics of anoptical recording medium having a SnGeSb type recording layer, when10-times velocity recording is carried out by another prescribedrecording method.

FIG. 38 presents data showing recording characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 24-times velocities by another prescribed recordingmethod.

FIG. 39 presents data showing overwriting characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 24-times velocities by another prescribed recordingmethod.

FIG. 40 presents data showing recording characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 32-times velocities by another prescribed recordingmethod.

FIG. 41 presents data showing overwriting characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 32-times velocities by another prescribed recordingmethod.

FIG. 42 presents data showing the linear velocity dependency of variousparameters when n is at least 4.

FIG. 43 presents data showing the linear velocity dependency of variousparameters when n=3.

FIG. 44 presents data showing recording characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 24-times velocities by another prescribed recordingmethod.

FIG. 45 presents data showing overwriting characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 24-times velocities by another prescribed recordingmethod.

FIG. 46 presents data showing recording characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 32-times velocities by another prescribed recordingmethod.

FIG. 47 presents data showing overwriting characteristics at therespective linear velocities, when recording was carried out on the samemedium at 8- to 32-times velocities by another prescribed recordingmethod.

FIG. 48 presents an example of data showing recording characteristicswhen recording was carried out on the same medium by various recordingmethods.

FIG. 49 presents an example of data showing overwriting characteristicswhen recording was carried out on the same medium by various recordingmethods.

FIG. 50 presents another example of data showing recordingcharacteristics when recording was carried out on the same medium byvarious recording methods.

FIG. 51 presents another example of data showing overwritingcharacteristics when recording was carried out on the same medium byvarious recording methods.

FIG. 52 presents data showing recording characteristics at the variouslinear velocities when recording was carried out on the same medium at8- to 24-times velocities by another prescribed recording method.

FIG. 53 presents data showing overwriting characteristics at the variouslinear velocities when recording was carried out on the same medium at8- to 24-times velocities by another prescribed recording method.

FIG. 54 presents data showing recording characteristics at the variouslinear velocities when recording was carried out on the same medium at8- to 24-times velocities by another prescribed recording method.

FIG. 55 presents data showing overwriting characteristics at the variouslinear velocities when recording was carried out on the same medium at8- to 24-times velocities by another prescribed recording method.

FIG. 56 presents data showing overwriting characteristics at the variouslinear velocities when recording was carried out on the same medium at8- to 24-times velocities by another prescribed recording method.

FIG. 57 presents data showing overwriting characteristics at the variouslinear velocities when recording was carried out on the same medium at8- to 24-times velocities by another prescribed recording method.

FIG. 58 presents data showing recording characteristics, when 24-timesvelocity recording was carried out by another prescribed recordingmethod on two types of rewritable optical recording media havingdifferent reflective layers.

FIG. 59 presents data showing recording characteristics, when 8-timesvelocity recording was carried out by another prescribed recordingmethod on two types of rewritable optical recording media havingdifferent reflective layers.

FIG. 60 presents another example of data showing recordingcharacteristics, when recording was carried out on the same medium atrecording linear velocities from 8-times velocity to 32-times velocity.

FIG. 61 presents another example of data showing overwritingcharacteristics, when recording was carried out on the same medium atrecording linear velocities from 8-times velocity to 32-times velocity.

FIG. 62 presents data showing recording characteristics, when recordingwas carried out at 10-times velocity by employing one embodiment of therecording method of the present invention.

FIG. 63 presents data showing overwriting characteristics, whenrecording was carried out at 10-times velocity by employing oneembodiment of the recording method of the present invention.

FIG. 64 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 6-times velocity by another prescribed recordingmethod.

FIG. 65 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 2.5-times velocity by another prescribed recordingmethod.

FIG. 66 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 6-times velocity by another prescribed recordingmethod.

FIG. 67 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 2.5-times velocity by another prescribed recordingmethod.

FIG. 68 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 8-times velocity by another prescribed recordingmethod.

FIG. 69 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 3-times velocity by another prescribed recordingmethod.

FIG. 70 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 10-times velocity by another prescribed recordingmethod.

FIG. 71 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 12-times velocity by another prescribed recordingmethod.

FIG. 72 presents data showing recording characteristics when recordingwas carried out on a rewritable optical recording medium (RW-DVD) of thepresent invention at 4-times velocity by another prescribed recordingmethod.

EMBODIMENTS OF THE PRESENT INVENTION

1. With Respect to the Characteristics of the Medium 1-1. In the Case ofCD-RW

In a case where the present invention is to be applied to CD-RW, as alinear velocity being a velocity of a beam spot of a recording laserbeam to the medium, 1.2 m/s to 1.4 m/s, particularly 1.2 m/s, is used asthe reference velocity V₁ i.e. 1-time velocity.

Firstly, disks according to the first and second aspects of the presentinvention will be described.

A rewritable optical recording medium of the present invention isusually of a disk-shape. And, a portion in a crystalline state of thephase-change type recording layer is in an unrecorded or erased state,and a portion in an amorphous state is in a recorded state. Informationto be recorded comprises signals EFM modulation by being irradiated witha recording beam such as a laser beam to form amorphous marks. A usuallyspiral groove is formed on the substrate of the medium. The amorphousmarks are usually formed in this groove. Here, the groove is meant for abottom of a recess for guiding a laser beam, formed on the substratesurface, which is a face closer as viewed from the incident side of therecording/retrieving laser beam. The groove is preferably wobbling in aradial direction at a frequency based on a carrier frequency whichbecomes 22.05 kHz as calculated as 1-time velocity, and such a groove iscalled a wobbling groove. And, the above carrier frequency isfrequency-modulated with a frequency of ±1 kHz, and by this fine changein frequency, address information on the disk is incorporated asabsolute time information. Such absolute time information is called ATIP(absolute time in pre-groove) signal.

This wobbling groove can be formed by forming it on a stamper at alinear velocity of 1-time velocity of CD in a CLV mode and theninjection molding a substrate based on this stamper. To increase therecording capacity, a wobbling groove is usually formed so that thecarrier frequency would be 22.05 kHz at a linear velocity of 1.2 m/s(with an allowance of ±0.1 m/s).

When data are to be recorded, the reference clock period T will be areference, and data will be recorded by forming marks and spaces(between marks) having various time lengths corresponding to integralmultiple lengths of the reference clock period. In EFM modulation, markshaving time lengths of from 3T to 11T are usually formed. Further, it iscommon that the reference clock period T is changed in inverseproportion to the recording linear velocity.

The inverse number of the reference clock period T is called a referenceclock frequency, and the reference clock frequency at 1-time velocity ofCD (linear velocity of from 1.2 m/s to ¼ m/s) corresponds to 1 channelbit of data and is usually 4.3218 MHz. This reference clock frequency isjust 196 times the reference frequency of 22.05 kHz of the abovewobbling.

The reference clock period T at 1-time velocity usually becomes1/(4.3218×10⁶)=231×10⁻⁹ (sec)=231 (nsec).

In the following description, the product VT of the reference clockperiod T and the linear velocity V is constant irrespective of thelinear velocity, unless otherwise specified.

FIG. 2(a) shows a schematic view of a retrieving waveform (an eyepattern) of EFM modulation signals to be used for a CD family includingCD-RW. In this eye pattern, all retrieving waveforms of amorphous marksand spaces in crystalline state, of from 3T to 11T, are randomlycontained. The retrieving waveforms are waveforms as observed on anoscilloscope when the reflected light intensities are taken out asvoltage signals. In such a case, the retrieving signals contain a directcurrent component.

One having the top I_(top) of the eye pattern converted to areflectivity to an incident light is the top value R_(top) ofreflectivity corresponding to a space, and one having the amplitude I₁₁of the eye pattern (for practical purpose, the amplitude of 11T mark)normalized by I_(top), is the modulation m₁₁ of the eye pattern of arecord signal represented by the following formula (1) (in thisspecification, m₁₁ may sometimes be referred to simply as a modulation).m ₁₁ =I ₁₁ /I _(top)×100 (%)  (1)

In the present invention, the modulation m₁₁ is from 60% to 80%. Themodulation depends upon the optical resolution and tends to be observedto be large by an optical system having a high NA. Therefore, in thepresent invention, a modulation m₁₁ is taken when recording is carriedout by irradiating a laser beam having a wavelength of about 780 nmthrough an optical system having a numerical aperture NA of 0.5.However, the wavelength is not required to be strictly 780 nm, and itmay be within a range of from about 775 to 795 nm.

The larger the signal amplitude I₁₁, the better. However, if it is toohigh, the gain of the amplifier in the signal retrieving system tends tobe extremely saturated, and accordingly, the upper limit of m₁₁ is 80%,preferably 78%, more preferably about 75%. On the other hand, if it istoo small, the signal-to-noise ratio (SN ratio) tends to be low, andaccordingly, the lower limit is 60%, preferably 62%, more preferablyabout 65%. Further, R_(top) is within a range of from 15 to 25%,preferably from 15 to 20%, more preferably from 16 to 19%. Further, itis preferred that the asymmetry value Asym as defined by the followingformula (2):Asym=(I _(slice) /I ₁₁−½) (%)  (2)is preferably as close as possible to 0, but it is usually within arange of ±10%. Here, I_(slice) is the potential difference between thecenterline 2001 of I and the bottom 2002 of the envelope curve in FIG.2(a), and I₁₁ is a voltage between the top 2003 and the bottom 2002 ofthe envelop curve.

The jitter and deviation of each of mark lengths and space lengths offrom 3T to 11T to be used for EFM modulation are determined as follows.Namely, the deviation of each of mark lengths and space lengths of from3T to 11T is a deviation from a prescribed value of an average value ofmark lengths or space lengths (nT; n=3 to 11), obtained by taking out aRF component by passing the retrieving signals in FIG. 2(a) through ahighpass filter, followed by DC-splicing using, as a threshold value,the 0 level which will be the substantial center value of the signalamplitudes, and the jitter is the standard deviation (jitter) thereof. Adetailed measurement method is prescribed in Red Book as CD standards,Orange Book as CD-RW standards or “CD Family” (published by OHM Co.,Apr. 25, 1996). In the present invention, the jitter is preferably suchthat when retrieving is carried out at 1-time velocity (the referenceclock period: 231 nsec), the jitter value is at most 35 nsec, preferablyat most 30 nsec, more preferably at most 25 nsec.

Usually, jitter of 3T mark length or space length tends to have theworst value among 3T to 11T in many cases. Further, jitter of 3T spacelength tends to have a worse value than jitter of 3T mark in many cases.

In the present invention, the deviation is usually at most ±40 nsec with3T and at most ±60 nsec with 11T. Further, with respect to 4T to 10T,the deviation will be a value obtained by complementing at most ±40 nsecand at most ±60 nsec as prescribed for 3T and 11T. In any case, thedeviation is acceptable if it is within a range of about ±20% of thereference clock period T.

With respect to the quality of signals after recording, it is preferredthat the same characteristics as specified in the current standards arebasically satisfied. Specifically, it is preferred to satisfy thecontent disclosed in Orange Book, Part 3.

By controlling the modulation m₁₁ the top value R_(top) of reflectivityand the jitter within the above-mentioned values, a medium recorded at ahigh velocity at a level of at least 24-times velocity, can be retrievedby a retrieving system for conventional CD-RW, while maintaininginterchangeability with conventional CD-RW standards.

With the rewritable optical recording medium of the present invention,it is preferred that in the recording at a linear velocity of 24-timesvelocity, when a simple periodic signal comprising 3T mark (a markhaving a time length of 3T, where T is the data reference clock period)and a 3T space (a space between marks, having a time length of 3T), isrecorded, and then, a simple periodic signal comprising a 11T mark (amark having a time length of 11T) and a 11T space (a space betweenmarks, having a time length of 11T), is overwritten, the erase ratio ofthe 3T mark is at least 20 dB. Such erase ratio is more preferably atleast 25 dB. Further, also at 32-times velocity, such erase ratio is atleast 20 dB, more preferably at least 25 dB. The higher such erase ratioat a high linear velocity, the higher the recrystallization speed at thetime of erasing amorphous marks, whereby with such a medium, overwritingof EFM signals at a high linear velocity is possible. For example, ifsuch erase ratio at 32-times velocity is set to be at least 20 dB, it isnot only possible to obtain good characteristics when used at 32-timesvelocity, but also possible to obtain good characteristics also whenused at less than 24-times velocity. Here, to record the simple periodicsignal comprising a 3T mark and a 3T space (between marks) and tooverwrite the simple periodic signal comprising a 11T mark and a 11Tspace, a recording method of the after-mentioned recording method CD1-1or 1-2 is employed. At the time of recording the simple periodicalsignal comprising a 3T mark and 3T space (between marks), 3T mark isrecorded by a writing power comprising one writing pulse Pw and asubsequent off-pulse Pb (0<Pb<1 mW), and at other sections, an erasingpower Pe is irradiated. Pw is a power to melt the recording layer, andPb is a cooling power to quench the melted region to form an amorphousstate. At the time of overwriting the simple periodic signal comprisinga 11T mark and a 11T space, a 11T mark is recorded by repeating awriting power comprising five writing pulses Pw and off-pulses Pb(0<Pb<1 mW) accompanying individual Pw, and at other sections, anerasing power Pe is irradiated. In overwriting 3T data and 11T data, thesame Pe and Pw are used, and the Pe dependency of the erase ratio ismeasured by changing Pe while maintaining Pe/Pw to be constant within arange of from 0.2 to 0.6, to confirm that at some Pe, the erase ratiobecomes at least 20 dB, preferably at least 25 dB. The erase ratio isone obtained by measuring the decrease of the carrier level of 3T databetween before and after the overwriting of the 11T data, by dB unit.

In any case, recording is carried out in the same groove, and usually,recording is carried out in a groove corresponding to one round.

If the erase ratio is sufficient at the upper limit within the linearvelocity range for overwriting, there will be no possibility that theerase ratio becomes deficient on a lower linear velocity side. Namely,the time for irradiation of the recording layer with a laser beam havinga wavelength of λ focused by an object lens having a numerical apertureNA moving at a linear velocity V, is normalized by λ/(NA·V), whereby theirradiation time increases as the linear velocity is low, and the timerequired for recrystallization can sufficiently be secured.

Further, as a recording method in the case of measuring the overwritingerase ratio by overwriting a 3T mark and a 11T mark, either one of theafter-mentioned recording methods CD1-1, 1-2 and 1-3, may be employed.However, it is particularly preferred to employ the recording methodCD1-3. In a case where the recording method CD1-3 is employed, it is notparticularly necessary to employ recording conditions where jitter islow, in the measurement of the erase ratio, and at the time of recordinga 11T mark, a tentative value of β_(m)′=0.5 may be employed.

Further, in the method for measuring the erase ratio, there may be acase where the reduction of the carrier level of the recorded marks ismeasured by a decibel value, while irradiating an erasing power Pe in adirect current (DC) fashion, and this is called a DC erase ratio. In themeasurement of the DC erase ratio, an erase ratio is employed in a casewhere the maximum erase ratio can be obtained while Pe is variable. Ascompared with the above-mentioned overwriting erase ratio, it maysometimes take a higher value by from 1 to 2 dB. If such a correctionvalue is taken into consideration, the measurement of the overwritingerase ratio may be substituted by the measurement of the DC erase ratio.

Further, when the archival life of the recording medium is representedby the time until the jitter of record signals previously recorded willreach 35 nsec (nano seconds) in retrieving at 1-time velocity, thearchival life at a temperature of 80° C. under a relative humidity of85%, is preferably at least 200 hours, more preferably at least 500hours.

Further, in the present invention, in order to satisfy the abovecharacteristics, when an accelerated test at a temperature of at least105° C. is applied as a condition where evaluation can be carried out ina shorter time, each of the modulation m₁₁ and the top value R_(top) ofreflectivity in a crystalline state (in this specification, this valuemay sometimes be referred to simply as R_(top)) maintains preferably atleast 80%, more preferably at least 90% of the initial value even uponexpiration of 3 hours in the accelerated test environment at atemperature of 105° C., because such a requirement is satisfied bycurrently commercially available CD-RW for from 1 to 4-time velocity.Especially when m₁₁ after the above accelerated test is made to maintainpreferably at least 80%, more preferably at least 90% of the initialvalue, the crystallization temperature of the recording layer which willbe described hereinafter, can be made to be at least about 150° C.

The definitions for the modulation m₁₁, R_(top), the jitter of each markor space between marks, the deviation, the asymmetry value, the eraseratio, etc. at the linear speed or linear velocity V (at this paragraph,V represents a linear velocity of 24-times velocity or 32-timesvelocity) in the present invention, are given from record signalsobtained by recording EFM modulation signals by overwriting 10 times byone recording method selected from the conditions of the followingrecording methods CD1-1 and CD1-2 while maintaining the reference clockperiod T to satisfy VT=V₁T₁, where V₁ is a reference velocity (1-timevelocity) which is set to be a linear velocity of 1.2 m/s, and T₁ is 231nsec, followed by retrieving at 1-time velocity.

Recording Method CD1-1:

A laser beam having a wavelength of 780 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.5, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.2 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁+Δ₁ (whereΔ₁=0.3 to 0.6), α_(i)=αc (where i is an integer of from 2 to m−1),β_(i−1)′+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.3 to 0.6, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 20 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁, Δ_(m−1),Δ_(m−1), α_(m) and Δ_(m) are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′, β₂ and β₂′ are made to be equal toα₁, α₁′, α₃, α₃′, β₃ and β₃′ in the case where m is 3, respectively, β₁is made to be equal to either β₁ or β₂ in the case where m is 3, and β₁′is made to be equal to either β₁′ or β₂ ′ in the case where m is 3(provided that a deviation of about ±10% is allowable), and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out;

Recording Method CD1-2:

A laser beam having a wavelength of 780 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.5, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T so that Σ_(i)(α_(i)+β_(i))=n−j,in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2 (where i is an integerof from 2 to m−1, and α_(i) takes a constant value αc between 0.7 to 1.2irrespective of such i), β₁+α₂=1.7 to 2.3, β_(i−1)+α_(i)=2 (where i isan integer of from 3 to m−1), β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to1.2, and β_(m)=0 to 2, and for a record mark of n=2m+1 (where m is aninteger of at least 3), of which the time length (n−k)T (where k is areal number of from −2.0 to 2.0) is divided into m sections of α_(i)′Tand β_(i)′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . . , α_(m)′T andβ_(m)′T, so that Σ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁,β₁′=β₁, α_(i)′=αc (where i is an integer of from 2 to m−1),β_(i−1)′+α_(i)′=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.5 to 1.2, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 20 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), β₁(=β₁′), αc, β_(m−1), Δ_(m−1), α_(m),β_(m) and Δ_(m)′ are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, β₁′, α₂, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₂, β₂′, α_(3, α) ₃′, β₃ and β₃′ in the case where mis 3, respectively (provided that a deviation of about ±10% isallowable), and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section Δ₁′T is carried out.

Here, Σ_(i)(α_(i)+β_(i)) or the like means to take the sum from 1 to mwith respect to i.

In the present invention, with a CD-RW disk rewritable at 24-timesvelocity or 32-times velocity of the above reference linear velocity, itis preferred that at least one of 8-times velocity, 10-times velocity,12-times velocity, 16-times velocity and 20-times velocity of thereference linear velocity, the modulation m₁₁, R_(top), the jitter ofeach mark or space between marks, the deviation, the asymmetry value andthe value of the erase ratio will be within the above-mentionednumerical value ranges.

Further, it is preferred that at any linear velocity between V_(min) andV_(max), where V_(min) is a linear velocity of any one selected from8-times velocity, 10-times velocity, 12-times velocity, 16-timesvelocity and 20-times velocity, and V_(max) is a linear velocity ofeither 24-times velocity or 32-times velocity, the modulation m₁₁,R_(top), the jitter, the deviation, the asymmetry value and the value ofthe erase ratio will be within the above numerical value ranges, wherebyrecording by the after-mentioned P-CAV or CAV system will be possible.

Here, specific values of the modulation m₁₁, R_(top), the jitter, thedeviation, the asymmetry value, the erase ratio, etc. at 8-timesvelocity, 10-times velocity, 12-times velocity, 16-times velocity or20-times velocity, are measured as follows. Namely, they are given fromrecord signals obtained by recording EFM modulation signals byoverwriting 10 times by one recording method selected from theconditions of the following recording methods CD2-1 and 2-2 at any oneof 8-times velocity (8V₁), 10-times velocity (10V₁), 12-times velocity(12V₁) 16-times velocity (16V₁) and 20-times velocity (20V₁) of thereference velocity V₁ (1-time velocity) which is set to be a linearvelocity of 1.2 m/s, while maintaining the data reference clock period Tto satisfy VT=V₁T₁ (where T₁ is 231 nsec, and V is any one of 10 V₁, 12V₁, 16 V₁ and 20 V₁), followed by retrieving at 1-time velocity.

Recording Method CD2-1:

A laser beam having a wavelength of 780 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.5, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.1 to 1, α_(i)=0.1 to 1(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.1 to 1 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.1 to 1, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁Δ₁(where Δ₁=0.3to 0.6), α_(i)′=αc (where i is an integer of from 2 to m−1),β_(i−1)′+α_(i)′=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.3 to 0.6, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 20 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁, β_(m−1),Δ_(m−1), α_(m) and Δ_(m) are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′, β₂ and β₂′ are made to be equal toα_(i), α₁′, α₃, α₃′, β₃ and β₃′ in the case where m is 3, respectively,β₁ is made to be equal to either β₁ or β₂ in the case where m is 3, andβ₁′ is made to be equal to either β₁′ or β₂′ in the case where m is 3(provided that a deviation of about ±10% is allowable), provided thatwith respect to β₂′, the value may further be changed within a range of±0.5, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out;

Recording Method CD2-2:

A laser beam having a wavelength of 780 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.5, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α_(i)=0.1 to 1, α_(i)=0.1 to 1(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.1 to 1 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.1 to 1, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁, α_(i)′=αc(where i is an integer of from 2 to m−1), β_(i−1)′+α_(i)′=2 (where i isan integer of from 3 to m−1), β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 0.6), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)≦0.6),Δ_(mm)=Δ_(m−1)+Δ_(m)=0.5 to 1.2, and β_(m)′=β_(m)+Δ_(m)′ (where Δ_(m)′=0to 1), a recording laser beam having a constant writing power Pwsufficient to melt the recording layer (provided that Pw is from 20 to40 mW, and Pe/Pw=0.2 to 0.6) is applied within a time of α_(i)T andα_(i)′T (where i is an integer of from 1 to m), and a recording laserbeam having a bias power Pb of less than 1 mW is applied within a timeof β_(i)T and β_(i)′T (where i is an integer of from 1 to m); andfurther,

when m is at least 3, α₁(=α₁′), β₁(=β₁′), αc, β_(m−1), Δ_(m−1), α_(m),β_(m) and Δ_(m)′ are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂′, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₂, β₂′, α_(3, α) ₃′, β₃ and β₃′ in the case where mis 3, respectively (provided that a deviation of about ±10% isallowable), and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out.

Here, in the recording methods CD1-1, 1-2, 2-1 and 2-2, j and k may takedifferent values for every n. Further, Pw, Pb and Pe are at constantpower levels, and Pb≦Pe≦Pw. And by using recording methods CD1-1 and1-2, or recording methods CD2-1 and 2-2, recording of an EFM randompattern is carried out wherein while maintaining the Pe/Pw ratio to beconstant at a level between 0.2 and 0.6, Pw is changed between 20 and 40mW, so that at Pw where the best characteristics can be obtained, theabove-mentioned respective values of the jitters of the respective marklengths and the respective spaces between marks, m₁₁ and R_(top), may besatisfied. Here, the power values Pw, Pe, Pb, etc. are meant to bepowers of the main beams among the recording laser beams and excludepowers which are classified to be beams not directly related to therecording, like a servo beam for a servo operation in a so-called threebeam method. With respect to the Pe/Pw ratio, firstly a value between0.3 and 0.4 is employed, and as a result, if the above requirements form₁₁, R_(top), the asymmetry, the deviation, etc. are not satisfied, avalue between 0.2 and 0.3, or between 0.3 and 0.6, is employed.

Further, the laser beam power level at each of recording pulse sectionsα_(i)T and α_(i)′T and off-pulse sections β_(i)T and β_(i)′T, isconstant at Pw for the recording pulse sections and at Pb for theoff-pulse sections. However, in a case where superposed frequencies areapplied, Pw and Pb are defined by average powers at such sections.Further, unavoidable overshooting or undershooting due to a response ofa laser diode is allowable. The rising or falling of the recordingpulses α_(i)T and α_(i)′T is at most about 3 nsec, but preferably from 1nsec to 2 nsec.

Recording methods CD1-1 and 1-2 are ones having a further study added toa record pulse-dividing method as disclosed in JP-A-2001-331936 whereina recording pulse (Pw irradiation section) and an off-pulse (Pbirradiation section) are alternately generated in repeated periodshaving period 2T as the base. Namely, in the present invention, amongrecording strategies having the 2T period as the base, a recordpulse-dividing method which is particularly suitable for CD-RWoverwritable at 24- or 32-times velocity and which is particularlyindustrially useful, economical and simple, has been found. By using therecording pulse strategy of the present invention, it is possible toprovide a recording medium and a recording method therefor, whereby therecord quality can easily be maintained even when recorded by aplurality of drives and interchangeability can easily be secured.

Accordingly, in the present invention, variable parameters and theirranges in the record pulse-dividing method using period 2T as the base,are defined. And, in the present invention, among many parameters in therecord pulse-dividing method using period 2T as the base, the minimumparameters required to maintain a good record quality at 24-timesvelocity or 32-times velocity, have been found, and they are used asvariable. If the number of variable parameters is increased, it becomesrelatively easy to accomplish good recording at 24-times velocity or32-times velocity. However, to make many parameters to be variablesimply makes the design of the electronic circuit (integrated circuit)complicated for generating pulses in a recording device to carry outrecording on the optical recording medium. Therefore, in the presentinvention, the minimum parameters have been found which make it possibleto realize CD-RW capable of carrying out 24-times velocity recording or32-times velocity recording while simplifying the design of theelectronic circuit (integrated circuit).

The minimum parameters to be variable to carry out good recording at24-times velocity or 32-times velocity, can be realized for the firsttime by carrying out a study on a recording medium overwritable at24-times velocity or 32-times velocity and a study on a pulse-dividingrecording method, while feeding back the respective knowledges mutually.Thus, the present invention has been accomplished by a high level ofcreation such that the recording medium and the recording method aresimultaneously realized.

By such studies, in the present invention, it has been made possible topresent a CD-RW recording medium and a recording method having highrecording and retrieving interchangeability within a very wide range oflinear velocities ranging from 8- or 10-times velocity to 24- or32-times velocity, which have not heretofore been realized.

In the case of EFM modulation of CD-RW, mark lengths nT may have caseswhere n=3, 4, 5, 6, 7, 8, 9, 10 and 11, which are divided into periodshaving 2T as the base where m=1, 2, 2, 3, 3, 4, 4, 5, and 5,respectively, so that recording is carried out by recording pulsesdivided into sets of m recording pulses and m off-pulses. In the presentinvention, in order to clearly define the CD-RW recording mediumoverwritable at 24-times velocity or 32-times velocity, the definitionsas shown by recording methods CD1-1 and 1-2, are adopted.

FIG. 3 is a graph showing one embodiment of the relation of therespective recording pulses in a case where the pulse-dividing methodsaccording to the above-mentioned recording methods CD1-1 and 2-1 are tobe carried out. In FIG. 3(b), the time widths of recording pulses andoff-pulses to form mark lengths 2 mT should formally be represented byα₁T, β₁T, αcT, . . . α_(m)T, β_(m)T, but for the sake of simple clearrepresentation of the graph, in FIG. 3(b), they are simply representedby α₁, β₁, αc, . . . β_(m), β_(m), i.e. by omitting the indication ofthe reference clock period T. The same applies also to FIG. 3(c).

As shown in FIG. 3, in the recording method of the present invention,consideration is given to whether the value which n in nT mark can take,is an odd number or an even number. Correction of mark length difference1T between an even number length mark and an odd number length mark forthe same division number m, is divided and allocated to an off-pulsesection β₁T next to the forefront recording pulse and to a recordingpulse periodic section (β_(m−1)+α_(m))T second from the last. Namely,the correction of mark length 1T is carried out by adjustment ofoff-pulse lengths β₁T and β_(m−1)T, and pulse α_(m)T of the lastrecording pulse section.

In FIG. 3, 300 represents the reference clock of period T.

FIG. 3(a) shows a pulse waveform corresponding to a record mark having alength of nT=2mT or nT=(2m+1)T, wherein symbol 301 corresponds to thelength of a record mark having a length of 2mT, and symbol 302corresponds to the length of a record mark having a length of (2m+1)T.In FIG. 3(a), a case where m=5, is shown.

In FIG. 3(b), 303 represents a waveform of divided recording pulses in acase where n=2m(=10). In FIG. 3(c), 307 represents a waveform of dividedrecording pulses in a case where n=2m+1(=11).

A value obtained by multiplying T_(d1) by T represents a delay time ofα₁T and α₁′T to the forward end T₀ of nT mark, and is usually constantirrespective of n. Further, usually, (T_(d1)+α₁)T=(T_(d1)+α₁′)T=2T tofacilitate synchronization of the recording pulse-generating circuit,but fine adjustment at a level of ±0.5T is further allowable. Especiallyfor 3T, 4T and 5T marks, it is preferred to carry out such fineadjustment of the delay time. The writing power level at recording pulsesections α_(i)T (i=1 to m) is constant at Pw; the bias power level atoff-pulse sections β_(i)T (i=1 to m) is constant at Pb; and the laserbeam irradiation power between marks i.e. at sections other than α_(i)T(i=1 to m) and β_(i)T (i=1 to m), is erasing power Pe which is constant.When n is an even number, at sections 304 excluding the forefrontrecording pulse and the last off-pulse (i.e. sections excluding 305 and306 in FIG. 3), (β_(i−1)+α_(i))T=2T (i=2 to m) i.e. constant, providedthat fine adjustment within a range of ±0.3T is allowable only withrespect to (β₁+α₂)T and (β_(m−1)+α_(m))T. On the other hand, in a casewhere n is an odd number, at sections 308 in FIG. 3,(β_(i−1)′+α_(i)′)T=2T (i=3 to m−1) i.e. constant.

In order to record two types of mark lengths where n=2m and 2m+1 withthe same division number, section (β₁+α₂)T and section (β_(m−1)+α_(m))Tare respectively increased or reduced by about 0.5T to adjust theirlengths. Due to an influence of heat interference, etc., such a valuemay not precisely be 0.5T, but will generally be within a range of from0.3T to 0.6T. β_(m) and β_(m)′ take substantially the same values withina range of from 0 to 2, but it is preferred that β_(m)=β_(m)′.

Referring to FIG. 3, recording corresponding to the mark lengthdifference 1T between even number length mark nT=10T and odd numberlength mark nT=11T, is carried out by the following operations 1 and 2.

Operation 1: As shown at section 309 in FIG. 3, Δ₁ is added to only β₁′of section (β₁′+α₂′)T to make β₁′=β₁+Δ₁ and α₂′=αc.

Operation 2: As shown at section 310 in FIG. 3, Δ_(mm)T is added tosection (β_(m−1)′+α_(m)′)T. Here, Δ_(mm)=Δ_(m−1)+Δ_(m), and Δ_(mm) isdivided into Δ_(m−1) and Δ_(m), so that Δ_(m−1) is added to β_(m−1), andΔ_(m) is added to α_(m). Here, Δ_(m−1) may be zero.

In the present invention, Δ_(m) is made to be larger than 0 (Δ_(m)>0) tomake α_(m)≠α_(m)′. By making Δ_(m) larger than 0, the shape of the rearend of record mark where n is an odd number among the same divisionnumber m, will be stabilized, whereby the jitter characteristics will beremarkably improved. More preferably, Δ_(m−1) and Δ_(m) are made to havesubstantially equal values. If Δ_(m−1) and Δ_(m) are made to besubstantially equal, it will be possible to simplify the design of theelectronic circuit (integrated circuit) to control generation of laserbeams (pulsed beams) for recording pulses and off-pulses in a recordingpulse strategy, while maintaining good jitter characteristics.

The above operations are carried out for m being at least 3, and Δ₁ andΔ_(mm) will take a value of from 0.3 to 0.6. The values of Δ_(m−1) andΔ_(m) are determined depending upon how Δ_(mm) is divided anddistributed, whereby Δ_(m−1) may take a value of from 0 to 0.6, andΔ_(m) may take a value of more than 0 and at most 0.6.

In order to increase or decrease section (β₁+α₂)T and section(β_(m−1)+α_(m))T, respectively, by about 0.5T to adjust their lengths,as mentioned above, Δ₁ and Δ_(mm) may be made to be 0.6, but Δ_(m−1) andΔ_(m) are preferably made to be a value of at most 0.5.

Now, with respect to recording method CD1-1, cases wherein m is at least3, m=2 and m=1, will, respectively, be described. Recording method CD2-1will be described later.

In recording method CD1-1, when m is at least 3, α₁′=α₁, β_(m)′=β_(m),and α_(i) and α_(i)′ are constant as αc irrespective of i where i=2 tom−1. Further, α_(m) and α_(m)′are also constant irrespective of m.Further, α₁(α₁′) is from 0.7 to 1.4, αc is from 0.7 to 1.2, and α_(m) isfrom 0.7 to 1.2.

Further, when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁,β_(m−1), Δ_(m−1) and Δ_(m) are constant irrespective of m. At 24-timesvelocity or 32-times velocity, αc=α_(i) (i=2 to m−1) is firstly made tobe a value within a range of from 0.9 to 1, and thereafter, fineadjustment is carried out within a range of ±0.2 (within a range of from0.7 to 1.2). For α₁ and α_(m), firstly the same value as αc is employed,and then, fine adjustment is carried out within a range of about 0.3 atthe maximum.

Here, when m=2 (n=4, 5), section (β₁+α₂)T may be understood to besection (β_(m−1)+α_(m))T, since m−1=1. In such a case, (β₁′+α₂′)T ismade to be longer by about 1T than (β₁+α₂)T. More specifically, α₁, α₁′,α₂, α₂′, β₂ and β₂′ are made to be equal to α₁, α₁′, α_(m), α_(m)′,β_(m) and β_(m)′ in the case where m is 3, respectively, β₁ is made tobe equal to either β₁or β_(m−1) in the case where m is 3, and β₁′ ismade to be equal to either β₁′ or β_(m−1)′ in the case where m is 3.Here, in spite of the expression “made to be equal”, a deviation at alevel of ±10% is allowable.

Thus, for an even number length mark, a recording pulse row 303 shown bya dotted line in FIG. 3(b) is obtained, and for an odd number lengthmark, a recording pulse row 307 shown by a dotted line in FIG. 3(c) isobtained.

Further, when m=1 (n=3), irradiation with a recording laser beamcomprising a pair of a writing power irradiation section α₁′T and a biaspower irradiation section β₁′T is carried out. In such a case, it ispreferred that α₁′ is made to be larger by from about 0.1 to 1.5 thanα₁′ in the case where m is at least 2, and β₁′ is made to be smallerthan β₁′ and to be the same as or larger than β_(m) and β_(m)′ in thecase where m is at least 2. Further, the range of β₁′ is preferably from0 to 2.

FIG. 16 is a graph showing one embodiment of the relation of therespective recording pulses in a case where the pulse-dividing methodsaccording to the above-mentioned recording methods CD1-2 and 2-2 are tobe carried out. In FIG. 16(b), the time widths of recording pulses andoff-pulses to form mark lengths 2 mT should formally be represented byα₁T, β₁T, αcT, . . . α_(m)T, β_(m)T, but for the sake of simple clearrepresentation of the graph, in FIG. 16(b), they are simply representedby α₁, β₁, αc, . . . α_(m), β_(m), i.e. the indication of the referenceclock period T is omitted. The same applies also to FIG. 16(c).

As shown in FIG. 16, consideration is given whether the value which n innT mark can take, is an odd number or an even number. Correction of marklength difference 1T between an even number length mark and an oddnumber length mark for the same division number m is divided andallocated to a recording pulse periodic section (β_(m−1)+α_(m))T and thelast off-pulse β_(m)T. Namely, the correction of mark length 1T iscarried out by adjustment of off-pulse lengths β_(m−1)T and β_(m)T, andpulse α_(m)T of the last recording pulse section.

As compared with the recording method shown in FIG. 3 (recording methodCD1-1, 2-1), in this recording method, recording pulses and off-pulsesto be changed as between even number and odd number marks, areconcentrated at the rear end portion of a mark, whereby there is notonly a merit in that the rear end jitter of a record mark can easily becontrolled, but also a merit in that the design of an electronic circuit(integrated circuit) to control generation of laser beams (pulsed beams)for recording pulses and off-pulses of the recording pulse strategy canbe simplified. Further, there is a merit that the number of parametersto be variable is small.

In FIG. 16, 400 represents the reference clock of period T.

FIG. 16(a) shows a pulse waveform corresponding to a record mark havinga length of nT=2mT or nT=(2m+1)T, wherein symbol 401 corresponds to thelength of a record mark having a length of 2mT, and symbol 402corresponds to the length of a record mark having a length of (2m+1)T.In FIG. 16(a), a case where m=5, is shown.

In FIG. 16(b), 403 represents a waveform of divided recording pulses ina case where n=2m(=10). In FIG. 3(c), 406 represents a waveform ofdivided recording pulses in a case where n=2m+1(=11).

A value obtained by multiplying T_(d1) by T represents a delay time tothe forward end T₀ of nT mark, of α₁T and α₁′T and is usually constantirrespective of n. Further, usually, (T_(d1)+α₁)T=(T_(d1)+α₁′)T=2T tofacilitate synchronization of the record pulse-generating circuit, butfine adjustment at a level of ±0.5T is further allowable. Especially for3T, 4T and 5T marks, it is preferred to carry out such fine adjustmentof the delay time. The writing power level at recording pulse sectionsα_(i)T (i=1 to m) is constant at Pw; the bias power level at off-pulsesections β_(i)T (i=1 to m) is constant at Pb; and the laser beamirradiation power between marks i.e. at sections other than α_(i)T (i=1to m) and β_(i)T (i=1 to m), is erasing power Pe which is constant. Whenn is an even number, at sections 404, (β_(i−1)+α_(i))T=2T (i=2 to m)i.e. constant, provided that fine adjustment within a range of ±0.3T isallowable only with respect to (β₁+α₂)T and (β_(m−1)+α_(m))T. On theother hand, in a case where n is an odd number, at sections 407 in FIG.16, (β_(i−1)′+α_(i)′)T=2T (i=2 to m−1) i.e. constant. However,(β₁′+α₂′)T is made to be equal to (β₁+α₂)T.

In order to record two types of mark lengths where n=2m and 2m+1 withthe same division number, section (β_(m−1)+α_(m))T is increased orreduced by about 1T to adjust its length. Due to an influence of heatinterference, etc., such a value may not precisely be 1T, but willgenerally be within a range of from 0.5 to 1.2T. β_(m) and β_(m)′ takesubstantially the same values within a range of from 0 to 2 (inrecording method CD2-2, β_(m)′=within 0 to 3). However, to correct theinfluence over the jitter at the rear end of a mark, β_(m) and β_(m)′are individually finely adjusted. Especially in recording method CD2-2,β_(m)′=β_(m)+Δ_(m)′, i.e. Δ_(m)′ (=0 to 1) is added to β_(m).

Referring to FIG. 16, recording corresponding to the mark lengthdifference 1T between even number length mark nT=10T and odd numberlength mark nT=11T, is carried out by the following operation 3.

Operation 3: As shown at section 408 in FIG. 16, Δ_(mm)T is added tosection (β_(m−1)+α_(m))T to obtain (β_(m−1)′+α_(m)′)T. Here,Δ_(mm)=Δ_(m−1)+Δ_(m), and Δ_(mm) is divided into Δ_(m−1) and Δ_(m), sothat Δ_(m−1) added to β_(m−1), and Δ_(m) is added to α_(m). Further, inorder to correct the influence to the jitter at the rear end of a mark,β_(m) is changed to β_(m)′ by an addition of Δ_(m)′.

The foregoing operation is carried out when m is at least 3, and Δ_(mm)takes a value of from 0.5 to 1.2. Δ_(m−1) and Δ_(m) may, respectively,take a value of from 0 to 0.6 depending upon how Δ_(mm) is divided anddistributed. Δ_(m−1), may be zero, Δ_(m) is made larger than 0 so thatα_(m)≠α_(m)′. When Δ_(m) is made larger than 0, the shape of the rearend of a record mark where n is an odd number among the same divisionnumber m, the jitter characteristics will be stable and remarkablyimproved. More preferably, Δ_(m−1) and Δ_(m) are made to havesubstantially equal values. When Δ_(m−1) and Δ_(m) are made to besubstantially equal, it will be possible to simplify the design of anelectronic circuit (integrated circuit) to control generation of pulsedbeams, while maintaining good jitter characteristics.

Δ_(m)′ takes a value of from 0 to 1, more preferably a value of from 0to 0.6. Especially at a linear velocity lower than 16-times velocity, itis preferred to make Δ_(m)′ larger than in the case of 24- or 32-timesvelocity. On the other hand, at 24- or 32-times velocity, it ispreferred to make Δ_(m)′=0.

Now, with respect to recording method CD1-2, cases where m is at least3, m=2 and m=1 will, respectively, be described. Recording method CD2-2will be described later.

In recording method CD1-2, when m is at least 3, α₁′=α₁ and β₁′=β₁, andα_(i) and α_(i)′ are constant as αc irrespective of i where i=2 to m−1.Further, α₁(=α₁′) takes a value within a range of from 0.7 to 1.4, andαc and α_(m) take a value within a range of from 0.7 to 1.2. Morepreferably, α₁(=α₁′), αc and α_(m) are within a range of from 0.7 to 1.

Further, when m is at least 3, α₁(=α₁′), β₁, αc, β_(m−1), Δ_(m−1),α_(m), Δ_(m), β_(m) and Δ_(m)′ are constant irrespective of m. At24-times velocity or 32-times velocity, it is preferred thatαc=α_(i)(i=2 to m) is firstly made to be 1, and then fine adjustmentwithin a range of ±0.2 is further carried out. For α₁ and α_(m),firstly, the same value as αc is employed, and fine adjustment iscarried out within a range of larger by about 0.3 at the maximum thanαc. Δ_(m) and Δ_(m−1) take about 0.4 as the initial value, and fineadjustment is carried out to obtain the prescribed mark lengths.Further, β_(m)′ at section 410 is firstly made to be equal to β_(m) atsection 405, and thereafter, fine adjustment is carried out.

Here, when m=2, (β₁′+α₂′)T is made longer by about 1T than (β₁+α₂)T.However, since m−1=1, they may be deemed to be (β_(m−1)′+α_(m)′)T and(β_(m−1)+α_(m))T, respectively. And, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ andβ₂′ are made to be equal to α₁, α₁′, β₂, β₂′, α₃, α₃′, β₃ and β₃′ in thecase where m=3, respectively. However, when m=2, α₁, α₁′, β₁, β₁′, α₂,α₂′, β₂ and β₂′ may further be finely adjusted within a range of about±10%.

Thus, for an even number length mark, recording pulse train 402 shown bya dotted line in FIG. 16(b) is obtained, and for an odd number lengthmark, recording pulse train 406 shown by a dotted line in FIG. 16(c) isobtained.

Further, when m=1 (n=3), irradiation with a recording laser beamcomprising a pair of a writing power irradiation section α₁′T and a biaspower irradiation section β₁′T is carried out. In such a case, α₁′ ispreferably made to larger by from about 0.1 to 1.5 than α₁′ in the casewhere m is at least 2. Further, the range of β₁′ is preferably from 0 to2.

In recording method CD2-1, an even number length mark and an odd numberlength mark are recorded by the same rule as in recording method CD1-1,and in recording method CD2-2, an even number length mark and an oddnumber length mark are recorded by the same rule as in recording methodCD1-2, but α_(i) and α_(i)′ (i=1 to m) are made to be values smallerthan in recording at a linear velocity of 24- or 32-times velocity andwithin a range of from 0.1 to 1. Consequently, β_(i) and β_(i)′ (i=1 tom) are made to be values larger than in recording at a linear velocityof 24-times velocity or 32-times velocity. Further, in the case ofrecording method CD2-2, especially Δ′_(m) is made to be variable withina range of from 0 to 1. Further, Δ_(m−1)+Δ_(m)Δ_(m)′ is preferably madeto be within a range of from 0.5 to 1.5.

When α_(i) and α_(i)′ in the case where the maximum linear velocityV_(max) in recording method CD1-1 or CD1-2 is made to be 24-timesvelocity or 32-times velocity, are represented by α_(i0) and α_(i0)′, ifthe same medium is subjected to recording at 8-times velocity, 10-timesvelocity, 12-times velocity, 16-times velocity or 20-times velocity(i.e. linear velocity V is any one of 8V₁, 10V₁, 12V₁, 16V₁ and 20V₁) byrecording method CD2-1 or recording method CD2-2, they are generally setto be α_(i)=η(V/V_(max))α_(i0), and α_(i)′=η(V/V_(max)) α_(i0)′, andthereafter, fine adjustment within a range of about ±0.1, is carriedout.

Here, η is a real number within a range of from 0.8 to 1.5.Particularly, a value within a range of from 1.0 to 1.3 is firstlyemployed, and thereafter, measurement is carried out by enlarging therange to be from 0.8 to 1.5.

Further, in recording method CD2-1 or 2-2, an exceptional rule may beapplied when n=5.

Namely, in recording method CD2-1, when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′,β₂ and β₂′ are made to be equal to α₁, α₁′, α₃(α_(m)), α₃′(α_(m)′),β₃(β_(m)) and β₃′(β_(m)′) in the case where m is 3, respectively, β₁ ismade to be equal to either β₁ or β₂ (β_(m−1)) in the case where m is 3,and β₁′ is made to be equal to either β₁′ or β₂′ (β_(m−1)′) in the casewhere m is 3. However, in spite of the expression “made to be equal”, adeviation at a level of ±10% is allowable. Further, with respect to β₂′when m=2, the value may further be changed within a range of ±0.5.

Further, in recording method CD2-2, when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′,α₂, α₂′, β₂ and β₂′ are made to be equal to α₁, α₁′, β₂(β_(m−1))β₂′(β_(m−1)′), α₃(α_(m)), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in thecase of m=3, respectively. However, in spite of the expression “made tobe equal”, a deviation at a level of ±10% is allowable. Further, β₁′ inthe case where n=3, is preferably made to be within a range of from 0 to3.

With respect to CD-RW expected to be used at a velocity of up to24-times velocity, the recording characteristics are defined for exampleat 10-times velocity and 24-times velocity, or at 12-times velocity and24-times velocity, and with respect to CD-RW expected to be used at avelocity of up to 32-times velocity, the recording characteristics at10-times velocity and 32-times velocity, the recording characteristicsat 12-times velocity and 32-times velocity, or the recordingcharacteristics at 16-times velocity and 32-times velocity, are,respectively, defined, whereby a medium suitable for the after-mentionedCAV recording system, P-CAV recording system or ZCLV recording system,can substantially univocally be defined from the viewpoint ofrecording/retrieving interchangeability among drives. In such a case, itis preferred that in recording method CD2-1 or 2-2 in the measurement ofa low linear velocity side, the values of α_(i), α_(i)′, β_(i) andβ_(i)′ are set so that they are generally proportional to the linearvelocity as mentioned above (α_(i)=η (V/V_(max))α_(i0), α_(i)′=η(V/V_(max))α_(i0)′), whereby the medium characteristics can better bedefined.

Thus, to define the characteristics of a rewritable optical recordingmedium at a plurality of recording linear velocities within differentrecording velocity ranges wherein the ratio between the minimum linearvelocity and the maximum linear velocity becomes at least two times, isa preferred method also with a view to securing recording/retrievinginterchangeability of a medium from the viewpoint of recording drives.It is particularly preferred to use recording method CD1-1 incombination with recording method CD2-1, and to use recording methodCD1-2 in combination with recording method CD2-2.

Thus, in the case of defining a medium within a specific range, it isparticularly preferred to combine recording method CD1-2 with recordingmethod CD2-2 to define rewritable CD-RW with the maximum linear velocityV_(max) of 24-times velocity or 32-times velocity.

Further, in a method for defining the medium characteristicscorresponding to such 32-times velocity or 24-times velocity, recordingmethod CD1-2may be further defined to present the following recordingmethod CD1-3, whereby the medium characteristics can more specificallybe defined. Thus, it is preferred that interchangeability can be securedwhen such a medium is subjected to recording by a plurality of recordingdevices.

Recording Method CD1-3:

For a mark length of m=at least 2, T_(d1)′=T_(d1)=2−αc, α_(i)′=α_(i)=αc(i=1 to m−1), β_(i)′=β_(i)=2−αc (i=1 to m−2), α_(m)=αc and β_(m−1)=2−αc,being constant, and β_(m−1)′=1+Δ_(m0) (0<Δ_(m0)≦0.6), α_(m)′=1+Δ_(m0)(0<Δ_(m0)≦0.6) and β_(m)′=β_(m)+Δ_(m)′, and Δ_(m0, Δ) _(m)′ are constantirrespective of m. Here, when m=2, β₁, β₁′, α₂, α₂′, β₂ and β₂′ aredeemed to be β₂(β_(m−1)), β₂′(β_(m−1)′), α₃(α_(m)), α₃′(α_(m)′)β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3. αc is from 0.7 to 1.2,more preferably from 0.7 to 1, particularly preferably from 0.9 to 1.

Here, it is particularly preferred to combine recording method CD1-3with the following recording method CD2-3 to define rewritable CD-RW tobe used at the maximum linear velocity V_(max) of 24-times velocity or32-times velocity.

Recording Method CD2-3:

For a mark length of m=at least 2 (n=4), T_(d1)′+α₁′=T_(d1)+α₁=2,α_(i)=αc (i=1 to m), α_(i)′=αc (i=1 to m−1), wherein αc=0.1 to 1,β_(i−1)+α_(i)=2 (i=2 to m) and β_(i−1)′+α_(i)′=2 (i=2 to m−1), andβ_(m−1)′=β_(m−1)+Δ_(m0) (0<Δ_(m0)≦0.6), α_(m)′=α_(m)+Δ_(m0)(0<Δ_(m0)≦0.6) and β_(m)′=β_(m)+Δ_(m)′ (Δ_(m)′=0 to 1), and further,Δ_(m0), β_(m) and Δ_(m)′ are constant irrespective of m. Here, when m=2,β₁, α₂ and β₂ are deemed to be β₂(β_(m−1)), β₃(β_(m)) and α₃′(α_(m)′) inthe case of m=3, respectively.

Recording methods CD1-3 and 2-3 are characterized in that when an oddnumber record mark is to be formed among an even number record mark andan odd number record mark having the same division number m, equal Δ_(m)(which is represented by Δ_(m0) in recording methods CD1-3 and 2-3) isimparted to an off-pulse section (β_(m−1)′) immediately before the lastand to the last recording pulse section (α_(m)′). By imparting equalΔ_(m) (which is represented as Δ_(m0) in recording methods CD1-3 and2-3), the design of an electronic circuit (integrated circuit) tocontrol generation of laser beams (pulsed beams) for recording pulsesand off-pulses of the recording pulse strategy for forming record marks,can be simplified, whereby it will be possible to reduce the costs forthe electronic circuit (integrated circuit).

It is particularly preferred to make Δ_(m) larger than 0 with a view tostabilizing the shape of the rear end portion of the record mark toimprove the jitter characteristics. Specifically, it is preferred thatit is made to be Δ_(m0) in recording methods 1-3 and 2-3, and Δ_(m0) ismade to be within a range of 0<Δ_(m0)≦0.6. In order to stabilize theshape of the rear end portion of the record mark, more preferred is thatΔ_(m0) is made to be within a range of 0<Δ_(m0)≦0.5.

Further, with a view to stabilizing the shape of the rear end portion ofa record mark where n is an odd number to improve the jittercharacteristics, Δ_(m)′ is preferably set to be within a range of0<Δ_(m)′≦1, more preferably 0<Δ_(m)′≦0.6, particularly preferably withina range of 0<Δ_(m)′≦0.5.

And, at each linear velocity, the optimum values of minimum parametersare determined in accordance with the procedure shown in FIG. 17. Thatis:

1) Provisional values Pw_(a), Pe_(a) and Pb_(a) are determined for Pw,Pe and Pb.

2) EFM signals composed solely of an even number mark and a space length(containing all of n=4, 6, 8 and 10) are recorded by irradiating Pw_(a),Pe_(a) and Pb_(a). As αc and β_(m) are variable, such αc and β_(m) aredetermined so that each mark length and each space length can beretrieved to have the prescribed length at the time of 1-time velocityretrieving within a range where m₁₁=0.6 to 0.8, and the jitter valuewill be 35 nsec.

3) Then, EFM signals obtained by adding an odd number mark length andspace length (including all of n=5, 7, 9 and 11) other than n=3, to theabove-mentioned FEM signals composed solely of an even number lengthmark and space length, are recorded by irradiation with Pw_(a), Pe_(a)and Pb_(a). For αc and β_(m), the above values are employed, andΔ_(m0)=Δ_(m−1)=Δ_(m) and Δ_(m)′ are variable, and such values aredetermined so that each mark length and each space length can beretrieved to have the prescribed length at the time of retrieving at1-time velocity, and the jitter value will be 35 nsec.

4) Finally, complete FEM signals having 3T mark and space added, arerecorded by irradiation with Pw_(a), Pe_(a) and Pb_(a). With respect tothe mark length of n=at least 2, the above-mentioned values of αc,β_(m), Δ_(m0)=β_(m−1)=Δ_(m) and Δ_(m)′ are employed. Only T_(d1)′, α₁′and β₁′ relating to n=3 are variable, and such values are determined sothat 3T mark length and space length can be retrieved to have theprescribed lengths at the time of retrieving at 1-time velocity and thejitter value will be 35 nsec.

5) Pw_(a) and Pe_(a) are variable, and fine adjustment of Pw and Pe iscarried out so that primarily, the jitter or the error rate will beminimum within a range where m₁₁=0.6 to 0.8. If, in each step of theabove procedure, m₁₁=0.6 to 0.8, and the jitter of 35 nsec, can not beobtained, such a medium is regarded as not satisfying the requirementsof the present invention.

Further, in FIG. 17, the Pe/Pw ratio and the initial value of Pw aredetermined as follows.

A repeating pattern (hereinafter referred to as 11T data) composedsolely of 11T mark length and space length, is recorded in an unrecordedstate groove with Pe=0 and only Pw being variable. In this state, Pwwhereby m₁₁ would be within a range of from 0.6 to 0.8, is determined toobtain the initial value Pw_(a). If m₁₁ increases beyond the range offrom 0.6 to 0.8 when Pw is increased, a Pw value whereby m₁₁ would beabout 0.7, is taken as the initial value Pw_(a). Then, Pe is irradiatedin a direct current fashion to the 11T data signals recorded by suchPw_(a), to measure the decrease of the carrier level of the 11T datasignals by dB (decibel value). This operation is repeated whileincreasing Pe within a range of Pe/Pw_(a)=0.2 to 0.6, and the first Pewhereby the decrease of the carrier level exceeds 25 dB, is taken as theinitial value Pe_(a) of Pe. As the initial value Pb_(a) of Pb, a powerequivalent to a retrieving laser beam power at a level where servo willbe stabilized at the time of retrieving with a power of 0<Pb_(a)<1 mW,is selected.

Further, in this specification, “overwriting” usually means to overwritenew data without returning once-recorded data to a uniform unrecorded orerased state by a certain specific treatment. However, in the presentinvention, also a case where recording is carried out in an initialuniform non-recorded or erased state is regarded as overwriting. Forexample, “overwriting ten times” in the case of evaluating thecharacteristics of an optical recording medium by means of the aboverecording method CD1-1, 1-2, 2-1 or 2-2, means to carry out the firstrecording (overwriting first time) in the initial crystalline state andthen carry out overwriting 9 times. The same applies in the followingdescription.

Further, the definition of “α_(i)+β_(i−1)=2” in recording methods CD1-1,1-2, 2-1 and 2-2, means that (α_(i)+β_(i−1)) is a time length twice thereference clock period T and may contain an error at a level offluctuation which inevitably results from the circuit design.Specifically, a difference at a level of 0.1T is regarded to besubstantially equal. Likewise, in the above description, for example, ina case where a specific α_(i) is made to be “constant” or “equal” toanother α_(i) or α_(i)′, inevitable fluctuation in practicing anelectronic circuit, is allowable.

Furthermore, even if the wavelength of the recording laser beam inrecording methods CD1-1, 1-2, 2-1 and 2-2 is fluctuated within a rangeof from about 775 to 795 nm, such will not be a serious problem, sincewith a phase-change medium, the wavelength dependency within such awavelength range is very small.

1-2. In the Case of RW-DVD

In a case where the present invention is to be applied to RW-DVD, as alinear velocity (speed) being a velocity of a beam spot of a recordinglaser beam to the medium, 3.49 m/s is used as the reference velocity V₁i.e. 1-time velocity.

Firstly, disks according to the first and second aspects of the presentinvention will be described.

A rewritable optical recording medium of the present invention isusually of a disk-shape. And, a portion in a crystalline state of thephase-change type recording layer is in an unrecorded or erased state,and a portion in an amorphous state is in a recorded state. Informationto be recorded comprises signals EFM+ modified by irradiating arecording beam such as a laser beam to form amorphous marks. A usuallyhelical groove is formed on the substrate of the medium. The amorphousmarks are usually formed in this groove. Here, the groove is meant for abottom of a recess for guiding a laser beam, formed on the substratesurface, which is a face closer as viewed from the incident side of therecording/retrieving laser beam.

When data are to be recorded, the reference clock period T will be areference, and data will be recorded by forming marks and spaces(between marks) having various time lengths corresponding to integralmultiple lengths of the reference clock period. In EFM+ modulation,marks having time lengths of from 3T to 14T are usually formed. Further,it is common that the reference clock period T is changed in inverseproportion to the recording linear velocity.

The inverse number of the reference clock period T is called a referenceclock frequency, and the reference clock frequency at 1-time velocity ofDVD (linear velocity of 3.49 m/s) corresponds to 1 channel bit of dataand is usually 26.15625 MHz.

The reference clock period T at 1-time velocity usually becomes1/(26.15625×10⁶)=38.2×10⁻⁹ (sec)=38.2 (nsec).

In the following description, the product VT of the reference clockperiod T and the linear velocity V is constant irrespective of thelinear velocity, unless otherwise specified.

FIG. 2(b) shows a schematic view of a retrieving waveform (an eyepattern) of EFM+ modified signals to be used for a DVD family includingDVD-RW. In this eye pattern, all retrieving waveforms of amorphous marksand spaces in crystalline state, of from 3T to 14T, are randomlycontained. The retrieving waveforms are waveforms as observed on anoscilloscope when the reflected light intensities are taken out asvoltage signals. In such a case, the retrieving signals contain a directcurrent component.

One having the top I_(14H) of the eye pattern converted to areflectivity to an incident light is the top value R_(top) ofreflectivity corresponding to a space, and one having the amplitude I₁₄of the eye pattern (for practical purpose, the amplitude of 14T mark)normalized by I_(14H), is the modulation m₁₄ of a record signalrepresented by the following formula (DVD1) (in this specification, m₁₄may sometimes be referred to simply as a modulation).m ₁₄ =I ₁₄ /I _(14H)×100 (%)  (DVD1)

In the present invention, the modulation m₁₄ is from 55% to 80%. Themodulation depends upon the optical resolving power and tends to beobserved to be large by an optical system having a large NA. Therefore,in the present invention, a modulation m₁₄ is taken when recording iscarried out by irradiating a laser beam having a wavelength of about 650nm through an optical system having a numerical aperture NA=0.60 orNA=0.65. However, the wavelength is not required to be strictly 650 nm,and it may be within a range of from about 630 to 665 nm.

The larger the signal amplitude I₁₄, the better. However, if it is toolarge, the gain of the amplifier in the signal retrieving system tendsto be extremely saturated, and accordingly, the upper limit of m₁₄ is80%, preferably 78%, more preferably about 75%. On the other hand, if itis too small, the signal-to-noise ratio (SN ratio) tends to be low, andaccordingly, the lower limit is 55%, preferably 60%, more preferablyabout 65%. Further, R_(top) is within a range of from 18 to 30%,preferably from 18 to 25%, more preferably from 19 to 23%. Further, itis preferred that the asymmetry value Asym as defined by the followingformula (DVD2):Asym=(((I _(14H) +I _(14L))/2−(I _(3H) +I _(3L))/2)/I ₁₄)×100(%)  (DVD2)is preferably as close as possible to 0, but it is usually within arange of from +10% to −5%.

Clock jitter of retrieving signals is one obtained by normalizing by thereference clock period T a standard deviation (jitter) of the differencein time against PLL clock of the leading edge and the trailing edge ofbinary signals obtained by passing the retrieving signals through anequalizer and LPF, followed by conversion to binary signals by a slicer.A detailed measurement method is prescribed in DVD-ROM standards orDVD+RW standards. In the present invention, with respect to the clockjitter, the clock jitter value when retrieving is carried out 1-timevelocity (reference clock period: 38.2 nsec) is at most 15%. Here, incurrent RW-DVD standards, the allowable value of this clock jitter isstipulated to be at most 9%, but in the present invention, up to 15% istaken as an allowable value, taking into consideration the improvementin performance of the DVD retrieving circuit in recent years. This clockjitter value is more preferably at most 12%, further preferably at most10%.

By controlling the modulation m₁₄, the top value R_(top) of reflectivityand the clock jitter within the above-mentioned values, a mediumrecorded at a high velocity at a level of at least 6-times velocity, canbe retrieved by a retrieving system for conventional phase-change typeDVD, while maintaining interchangeability with conventional phase-changetype DVD standards.

Further, in the following, the clock jitter in RW-DVD may sometimes bereferred to simply as jitter.

With the rewritable optical recording medium of the present invention,it is preferred that when at any one of 6-times velocity, 8-timesvelocity, 10-times velocity and 12-times velocity, a simple periodicsignal (referred to as 3T data) comprising a 3T mark and a 3T space (aspace between mark), is recorded, and then, a simple periodic signal(referred to as 14T data) comprising a 14T mark and a 14T space, isoverwritten, the erase ratio of the 3T mark is at least 20 dB,preferably at least 25 dB. Further, also at 12-times velocity, sucherase ratio is preferably at least 20 dB, more preferably at least 25dB. The higher such erase ratio at a high linear velocity, the higherthe recrystallization speed at the time of erasing amorphous marks,whereby with such a medium, overwriting of EFM+ signals at a high linearvelocity is possible. For example, if such erase ratio at 10-timesvelocity or 12-times velocity is set to be at least 20 dB, it is notonly possible to obtain good characteristics when used at 6-timesvelocity, but also possible to obtain good characteristics also whenused at less than 6-times velocity. Here, to record the simple periodicsignal comprising a 3T mark and 3T space (between marks) and tooverwrite the simple periodic signal comprising a 14T mark and a 14Tspace, a recording method of the after-mentioned recording method DVD1-1or 1-2 is employed. At the time of recording the simple periodicalsignal comprising 3T mark and 3T space (between marks), a 3T mark isrecorded by a writing power comprising one writing pulse Pw and asubsequent off-pulse Pb (0<Pb<1 mW), and at other sections, an erasingpower Pe is irradiated. Pw is a power to melt the recording layer, andPb is a cooling section to quench the melted region to form an amorphousstate. At the time of overwriting the simple periodic signal comprisinga 14T mark and a 14T space, a 14T mark is recorded by repeating awriting power comprising seven writing pulses Pw and off-pulses Pb(0<Pb<1 mW) accompanying individual Pw, and at other sections, anerasing power Pe is irradiated. In overwriting 3T data and 14T data, thesame Pe and Pw are used, and the Pe dependency of the erase ratio ismeasured by changing Pe while maintaining Pe/Pw to be constant within arange of from 0.2 to 0.6, to confirm that at some Pe, the erase ratiobecomes at least 20 dB, preferably at least 25 dB. The erase ratio isone obtained by measuring the decrease of the carrier level of 3T databetween before and after the overwriting of the 14T data, by dB unit.

In any case, recording is carried out in the same groove, and usually,recording is carried out in a groove corresponding to one round.

With respect to the erase ratio, if the erase ratio is sufficient at theupper limit within the linear velocity range for overwriting, there willbe no possibility that the erase ratio becomes deficient on a lowerlinear velocity side than usual. Namely, the time for irradiation of therecording layer with a laser beam having a wavelength of λ condensed byan object lens having a numerical aperture NA moving at a linearvelocity V, is standardized by λ/(NA·V), whereby the irradiation timeincreases as the linear velocity is low, and the time required forrecrystallization can sufficiently be secured.

Further, when the archival life of the recording medium is representedby the time until the jitter of record signals previously recorded willreach 12% in retrieving at 1-time velocity, the archival life at atemperature of 80° C. under a relative humidity of 85%, is preferably atleast 200 hours, more preferably at least 500 hours.

Further, in the present invention, in order to is satisfy the abovecharacteristics, when an accelerated test at a temperature of at least105° C. is applied as a condition where evaluation can be carried out ina shorter time, each of the modulation m₁₄ and the top value R_(top) ofreflectivity in a crystalline state maintains preferably at least 90% ofthe initial value even upon expiration of 3 hours in the acceleratedtest environment at a temperature of 105° C., because such a requirementis satisfied by currently commercially available DVD+RW for from 1 to2.4-time velocity.

The definitions for the modulation m₁₄, R_(top), the jitter, theasymmetry value, the erase ratio, etc. at the linear velocity V (at thisparagraph, V represents a linear velocity of 6-times velocity, 8-timesvelocity, 10-times velocity or 12-times velocity) in the presentinvention, are given from record signals obtained by recording EFM+modulation signals by overwriting 10 times by one recording methodselected from the conditions of the following recording methods DVD1-1and DVD1-2 while maintaining the data reference clock period T tosatisfy VT=V₁T₁, where V₁ is a reference velocity (1-time velocity)which is set to be a linear velocity of 3.49 m/s, and T₁ is 38.2 nsec,followed by retrieving at 1-time velocity.

Recording Method DVD1-1:

A laser beam having a wavelength of 650 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.65, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11 and 14),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.2 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁+Δ₁ (whereΔ₁=0.3 to 0.6), α_(i)′=αc (where i is an integer of from 2 to m−1),β_(i−1)′+α_(i)′=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.3 to 0.6, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 10 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), αc, β_(m)(=_(m)′), β₁, Δ₁, β_(m−1),Δ_(m−1), α_(m) and Δ_(m) are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′, β₂ and β₃′ are made to be equal toα₁, α₁′, α₃, α₃′, β₃ and β₃′ in the case where m is 3, respectively, β₁is made to be equal to either β₁ or β₂ in the case where m is 3, and β₁′is made to be equal to either β₁′ or β₂′ in the case where m is 3(provided that a deviation of about ±10% is allowable), and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out;

Recording Method DVD1-2:

A laser beam having a wavelength of 650 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.65, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11 and 14),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)′T and β_(i)′T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.7 to 1.4, α_(i)=0.7 to 1.2(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.7 to 1.2 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.7 to 1.2, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁, α_(i)′=αc(where i is an integer of from 2 to m−1), β_(i−1)′+α_(i)′=2 (where i isan integer of from 3 to m−1), β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 0.6), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)≦0.6),Δ_(mm)=Δ_(m−1)+Δ_(m)=0.5 to 1.2, and β_(m)′=β_(m), a recording laserbeam having a constant writing power Pw sufficient to melt the recordinglayer (provided that Pw is from 10 to 40 mW, and Pe/Pw=0.2 to 0.6) isapplied within a time of α_(i)T and α_(i)′T (where i is an integer offrom 1 to m), and a recording laser beam having a bias power Pb of lessthan 1 mW is applied within a time of β_(i)T and β_(i)′T (where i is aninteger of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), β₁(=β₁′), αc, β_(m−1), Δ_(m−1), α_(m),β_(m) and Δ_(m)′ are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₂, β₂′, α_(3, α) ₃′, β₃ and β₃′ in the case where mis 3, respectively, provided that in spite of the expression “made to beequal”, a deviation of about ±10% is allowable, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out.

Here, Σ_(i)(α_(i)+β_(i)) or the like means to take the sum from 1 to mwith respect to i.

In the present invention, with RW-DVD rewritable at 6-times velocity,8-times velocity, 10-times velocity or 12-times velocity of the abovereference linear velocity, it is preferred that at least one of 2-timesvelocity, 2.5-times velocity, 3-times velocity, 4-times velocity and5-times velocity of the reference linear velocity, the modulation m₁₄,R_(top), the jitter, the asymmetry value and the value of the eraseratio will be within the above-mentioned numerical value ranges.

Further, it is preferred that at any linear velocity between V_(min) andV_(max), where V_(min) is a linear velocity of any one selected from2-times velocity, 2.5-times velocity, 3-times velocity, 4-times velocityand 5-times velocity, of the above-mentioned reference velocity, andV_(max) is 6-times velocity, 8-times velocity, 10-times velocity or12-times velocity, of the reference velocity, the modulation m₁₄,R_(top), the jitter, the asymmetry value and the value of the eraseratio will be within the above numerical value ranges, whereby recordingby the after-mentioned P-CAV or CAV system will be possible.

Here, specific values of the modulation m₁₄, R_(top), the jitter, theasymmetry value, the erase ratio, etc. at 2-times velocity, 2.5-timesvelocity, 3-times velocity, 4-times velocity or 5-times velocity, aremeasured as follows. Namely, they are given from record signals obtainedby recording EFM+ modulation signals by overwriting 10 times by onerecording method selected from the conditions of the following recordingmethods DVD2-1 and 2-2 at any one of 2-times velocity (2V₁), 2.5-timesvelocity (2.5V₁), 3-times velocity (3V₁), 4-times velocity (4V₁) and5-times velocity (5V₁) of the reference velocity V₁ (1-time velocity)which is set to be a linear velocity of 3.49 m/s, while maintaining thedata reference clock period T to satisfy VT=V₁T₁ (where T₁ is 38.2 nsec,and V is any one of 2.5V₁, 3V₁, 4V₁ and 5V₁), followed by retrieving at1-time velocity.

Recording Method DVD2-1:

A laser beam having a wavelength of 650 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.65, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11 and 14),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.1 to 1, α_(i)=0.1 to 1(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.1 to 1 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.1 to 1, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁+Δ₁ (whereΔ₁=0.3 to 0.6), α_(i)′=αc (where i is an integer of from 2 to m−1),β_(i−1)′+α_(i)′=2 (where i is an integer of from 3 to m−1),β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0 to 0.6), α_(m)′=α_(m)+Δ_(m)(where 0<Δ_(m)≦0.6), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.3 to 0.6, and β_(m)′=β_(m),a recording laser beam having a constant writing power Pw sufficient tomelt the recording layer (provided that Pw is from 10 to 40 mW, andPe/Pw=0.2 to 0.6) is applied within a time of α_(i)T and α_(i)′T (wherei is an integer of from 1 to m), and a recording laser beam having abias power Pb of less than 1 mW is applied within a time of β_(i)T andβ_(i)′T (where i is an integer of from 1 to m); and further,

when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁, β_(m−1),Δ_(m−1), α_(m) and Δ_(m) are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′, β₂ and β₂′ are made to be equal toα₁, α₁′, α₃, α₃′, β₃ and β₃′ in the case where m is 3, respectively, β₁is made to be equal to either β₁ or β₂ in the case where m is 3, and β₁′is made to be equal to either β₁′ or β₂ ′ in the case where m is 3, herea deviation of about ±10% is allowable, provided that with respect toβ₂′, the value may further be changed within a range of ±0.5, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out;

Recording Method DVD2-2:

A laser beam having a wavelength of 650 nm is irradiated via an opticalsystem having a numerical aperture NA of 0.65, wherein when the timelength of one amorphous mark is represented by nT (where n is an integerof from 3 to 11 and 14),

between record marks, an erasing power Pe capable of crystallizing anamorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 3), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)′T and β_(i)′T comprising α₁′T,β₁′T, α₂′T, β₂T, . . . , α_(m)T and β_(m)T, so thatΣ_(i)(α_(i)+β_(i))=n−j, in the order of α₁=0.1 to 1, α_(i)=0.1 to 1(where i is an integer of from 2 to m−1, and α_(i) takes a constantvalue αc between 0.1 to 1 irrespective of such i), β₁+α₂=1.7 to 2.3,β_(i−1)+α_(i)=2 (where i is an integer of from 3 to m−1),β_(m−1)+α_(m)=1.7 to 2.3, α_(m)=0.1 to 1, and β_(m)=0 to 2, and for arecord mark of n=2m+1 (where m is an integer of at least 3), of whichthe time length (n−k)T (where k is a real number of from −2.0 to 2.0) isdivided into m sections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T,α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T, so thatΣ_(i)(α_(i)′+β_(i)′)=n−k, in the order of α₁′=α₁, β₁′=β₁, α_(i)′=αc(where i is an integer of from 2 to m−1), β_(i−1)′+α_(i)′=2 (where i isan integer of from 3 to m−1), β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 0.6), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)≦0.6),Δ_(mm)=Δ_(m−1)+Δ_(m)=0.5 to 1.2, and β_(m)′=β_(m)+Δ_(m)′ (where Δ_(m)′=0to 1), a recording laser beam having a constant writing power Pwsufficient to melt the recording layer (provided that Pw is from 10 to40 mW, and Pe/Pw=0.2 to 0.6) is applied within a time of α_(i)T andα_(i)′T (where i is an integer of from 1 to m), and a recording laserbeam having a bias power Pb of less than 1 mW is applied within a timeof β_(i)T and β_(i)′T (where i is an integer of from 1 to m); andfurther,

when m is at least 3, α₁(=α₁′), β₁(=β₁′), αc, β_(m−1), Δ_(m−1), α_(m)and Δ_(m)′ are constant irrespective of m,

when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₂, β₂′, α_(3, α) ₃′, β₃ and β₃′ in the case where mis 3, respectively, provided that a deviation of about ±10% isallowable, and

when m=1 (n=3), irradiation with a recording laser beam comprising apair of a writing power irradiation section α₁′T and a bias powerirradiation section β₁′T is carried out.

Here, in the recording methods DVD1-1, 1-2, 2-1 and 2-2, j and k maytake different values for every n. Further, Pw, Pb and Pe are atconstant power levels, and Pb≦Pe≦Pw. And by using recording methodsDVD1-1 and 1-2, or recording methods DVD2-1 and 2-2, recording of anEFM+ random pattern is carried out wherein while maintaining the Pe/Pwratio to be constant at a level between 0.2 and 0.6, Pw is changedbetween 10 and 40 mW, so that at Pw where the best characteristics canbe obtained, the above-mentioned respective values of the jitters, m₁₄and R_(top), may be satisfied. Here, the power values Pw, Pe, Pb, etc.are meant to be powers of the main beams among the recording laser beamsand extrude powers which are classified to be beams not directly relatedto the recording, like a servo beam for a servo operation in a so-calledthree beam method. With respect to the Pe/Pw ratio, firstly a valuebetween 0.3 and 0.4 is employed, and as a result, if the aboverequirements for m₁₄, R_(top), the asymmetry, etc. are not satisfied, avalue between 0.2 and 0.3, or between 0.3 and 0.6, is employed.

Further, the laser beam power level at each of recording pulse sectionsα_(i)T and α_(i)′T and off-pulse sections β_(i)T and β_(i)′T, isconstant at Pw for the recording pulse sections and at Pb for theoff-pulse sections. However, in a case where superposed frequencies areapplied, Pw and Pb are defined by average powers at such sections.Further, unavoidable overshooting or undershooting due to a response ofa laser diode is allowable. The rising or falling of the recordingpulses α_(i)T and α_(i)′T is at most about 2 nsec, but preferably from 1nsec to 2 nsec.

Recording methods DVD1-1 and 1-2 are ones having a further study addedto a record pulse-dividing method as disclosed in JP-A-2001-331936wherein a recording pulse (Pw irradiation section) and an off-pulse (Pbirradiation section) are alternately generated in repeated periodshaving period 2T as the base. Namely, in the present invention, amongrecording strategies having the 2T period as the base, a recordpulse-dividing method which is particularly suitable for phase-changetype rewritable DVD overwritable at 6- to 12-times velocity and which isparticularly industrially useful, economical and simple, has been found.By using the recording pulse strategy of the present invention, it ispossible to provide a recording medium and a recording method therefor,whereby the record quality can easily be maintained even when recordedby a plurality of drives and interchangeability can easily be secured.

Accordingly, in the present invention, variable parameters and theirranges in the record pulse-dividing method using period 2T as the base,are defined. And, in the present invention, among many parameters in therecord pulse-dividing method using period 2T as the base, the minimumparameters required to maintain a good record quality at 6-timesvelocity to 12-times velocity, have been found, and they are used asvariable. If the number of variable parameters is increased, it becomesrelatively easy to accomplish good recording at 6-times velocity to12-times velocity. However, to make many parameters to be variablesimply makes the design of the electronic circuit (integrated circuit)complicated for generating pulses in a recording device to carry outrecording on the optical recording medium. Therefore, in the presentinvention, the minimum parameters have been found which make it possibleto accomplish good recording at 6-times velocity to 12-times velocitywhile simplifying the design of the electronic circuit (integratedcircuit).

The minimum parameters to be variable to carry out good recording at6-times velocity to 12-times velocity, can be realized for the firsttime by carrying out a study on a recording medium overwritable at6-times velocity to 12-times velocity and a study on a pulse-dividingrecording method, while feeding back the respective knowledges mutually.Thus, the present invention has been accomplished by a high level ofcreation such that the recording medium and the recording method aresimultaneously realized.

By such studies, in the present invention, it has been made possible topresent a recording medium and a recording method having high recordingand retrieving interchangeability within a very wide range of linearvelocities ranging from 2- or 2.5-times velocity to 6- or 12-timesvelocity, which have not yet been realized.

In the case of EFM+ modulation of RW-DVD, mark lengths nT may have caseswhere n=3, 4, 5, 6, 7, 8, 9, 10, 11 and 14, which are, respectively,divided into periods having 2T as the base where m=1, 2, 2, 3, 3, 4, 4,5, 5 and 7, so that recording is carried out by recording pulses dividedinto sets of m recording pulses and m off-pulses. In the presentinvention, in order to clearly define the RW-DVD overwritable at 6-timesvelocity, 8-times velocity, 10-times velocity or 12-times velocity, thedefinitions as shown by recording methods DVD1-1 and 1-2, are adopted.

FIG. 3 is a graph showing one embodiment of the relation of therespective recording pulses in a case where the pulse-dividing methodsaccording to the above-mentioned recording methods DVD1-1 and 2-1 are tobe carried out. In FIG. 3(b), the time widths of recording pulses andoff-pulses to form mark lengths 2 mT should formally be represented byα₁T, β₁T, αcT, . . . α_(m)T, β_(m)T, but for the sake of simple clearrepresentation of the graph, in FIG. 3(b), they are simply representedby α₁, β₁, αc, . . . α_(m), β_(m), i.e. the indication of the referenceclock period T is omitted. The same applies also to FIG. 3(c).

As shown in FIG. 3, in the recording method of the present invention,consideration is given whether the value which n in nT mark can take, isan odd number or an even number. Correction of mark length difference 1Tbetween an even number length mark and an odd number length mark for thesame division number m is divided and allocated to an off-pulse sectionBIT next to the forefront recording pulse and a recording pulse periodicsection (β_(m−1)+α_(m))T second from the last. Namely, the correction ofmark length 1T is carried out by adjustment of off-pulse lengths β₁T andβ_(m−1)T, and pulse α_(m)T of the last recording pulse section.

In FIG. 3, 300 represents the reference clock of period T.

FIG. 3(a) shows a pulse waveform corresponding to a record mark having alength of nT=2mT or nT=(2m+1)T, wherein symbol 301 corresponds to thelength of a record mark having a length of 2mT, and symbol 302corresponds to the length of a record mark having a length of (2m+1)T.In FIG. 3(a), a case where m=5, is shown.

In FIG. 3(b), 303 represents a waveform of divided recording pulses in acase where n=2m(=10). In FIG. 3(c), 307 represents a waveform of dividedrecording pulses in a case where n=2m+1(=11).

A value obtained by multiplying T_(d1) by T represents a delay time tothe forward end T₀ of nT mark, of α₁T and α₁′T and is usually constantirrespective of n. Further, usually, (T_(d1)+α₁)T=(T_(d1)+α₁′)T=2T tofacilitate synchronization of the record pulse-generating circuit, butfine adjustment at a level of ±0.5T is further allowable. Especially for3T, 4T and 5T marks, it is preferred to carry out such fine adjustmentof the delay time. The writing power level at recording pulse sectionsα_(i)T (i=1 to m) is constant at Pw; the bias power level at off-pulsesections β_(i)T (i=1 to m) is constant at Pb; and the laser beamirradiation power between marks i.e. at sections other than α_(i)T (i=1to m) and β_(i)T (i=1 to m), is erasing power Pe which is constant. Whenn is an even number, at sections 304 excluding the forefront recordingpulse and the last off-pulse (i.e. sections excluding 305 and 306 inFIG. 3), (β_(i−1)+α_(i))T=2T (i=2 to m) i.e. constant, provided thatfine adjustment within a range of ±0.3T is allowable only with respectto (β₁+α₂)T and (β_(m−1)+α_(m))T. On the other hand, in a case where nis an odd number, at sections 308 in FIG. 3, (β_(i−1)′+α_(i)′)T=2T (i=3to m−1) i.e. constant.

In order to record two types of mark lengths where n=2m and 2m+1 withthe same division number, section (β₁+α₂)T and section (β_(m−1)+α_(m))Tare respectively increased or reduced by about 0.5T to adjust theirlengths. Due to an influence of heat interference, etc., such a valuemay not precisely be 0.5T, but will generally be within a range of from0.3T to 0.6T. β_(m) and β_(m)′ take substantially the same values withina range of from 0 to 2, but it is preferred that β_(m)=β_(m)′.

Referring to FIG. 3, recording corresponding to the mark lengthdifference 1T between even number length mark nT=10T and odd numberlength mark nT=11T, is carried out by the following operations 1 and 2.

Operation 1: As shown at section 309 in FIG. 3, Δ₁ is added to only β₁′of section (β₁′+α₂′)T to make β₁′=β₁+Δ₁ and α₂′=αc.

Operation 2: As shown at section 310 in FIG. 3, Δ_(mm)T is added tosection (β_(m−1)′+α_(m)′)T. Here, Δ_(mm)=Δ_(m−1)+Δ_(m), and Δ_(mm) isdivided into Δ_(m−1) and Δ_(m), so that Δ_(m−1) is added to β_(m−1) andΔ_(m) is added to Δ_(m). Here, Δ_(m−1) may be zero.

In the present invention, Δ_(m) is made to be larger than 0 (Δ_(m)>0) tomake α_(m)≠α_(m)′. By making Δ_(m) larger than 0, the shape of the rearend of record mark where n is an odd number among the same divisionnumber m, will be stabilized, whereby the jitter characteristics will beremarkably improved. More preferably, Δ_(m−1) and Δ_(m) are made to havesubstantially equal values. If Δ_(m−1) and Δ_(m) are made to besubstantially equal, it will be possible to simplify the design of theelectronic circuit (integrated circuit) to control generation of laserbeams (pulsed beams) for recording pulses and off-pulses in a recordingpulse strategy, while maintaining good jitter characteristics.

The above operations are carried out for m being at least 3, and Δ₁ andΔ_(mm) will take a value of from 0.3 to 0.6. The values of Δ_(m−1) andΔ_(m) are determined depending upon how Δ_(mm) is divided anddistributed, whereby Δ_(m−1), may take a value of from 0 to 0.6, andΔ_(m) may take a value of more than 0 and at most 0.6.

In order to increase or decrease section (β₁+α₂)T and section(β_(m−1)+α_(m))′T, respectively, by about 0.5T to adjust their lengths,as mentioned above, Δ₁, Δ_(m−1), Δ_(m) and Δ_(mm) may be made to be 0.6,but Δ₁, Δ_(m−1) and Δ_(m) are preferably made to be a value of at most0.5.

Now, with respect to recording method DVD1-1, cases wherein m is atleast 3, m=2 and m=1, will, respectively, be described. Recording methodDVD2-1 will be described later.

In recording method DVD1-1, when m is at least 3, α₁′=α₁, β_(m)′=β_(m),and α_(i) and α_(i)′ are constant as αc irrespective of i where i=2 tom−1. Further, α_(m) and α_(m)′ are also constant irrespective of m.Further, α₁(α_(m)′) is from 0.7 to 1.4, αc is from 0.7 to 1.2, and α_(m)is from 0.7 to 1.2.

Further, when m is at least 3, α₁(=α₁′), αc, β_(m)(=β_(m)′), β₁, Δ₁,β_(m−1) and Δ_(m) are constant irrespective of m. At 6-times velocity or8-times velocity, αc=α_(i) (i=2 to m−1) is firstly made to be a valuewithin a range of from 0.9 to 1, and thereafter, fine adjustment iscarried out within a range of ±0.2 (within a range of from 0.7 to 1.2).For α₁ and α_(m), firstly the same value as αc is employed, and then,fine adjustment is carried out within a range of about 0.3 at themaximum.

Here, when m=2 (n=4, 5), section (β₁+α₂)T may be understood to besection (β_(m−1)+α_(m)) T, since m−1=1. In such a case, (β₁′+α₂′)T ismade to be longer by about 1T than (β₁+α₂)T. More specifically, α₁, α₁′,α₂, α₂′, β₂ and β₂′ are made to be equal to α₁, α₁′, α_(m), α_(m)′,β_(m) and β_(m)′ in the case where m is 3, respectively, β₁ is made tobe equal to either β₁ or β_(m−1) in the case where m is 3, and β₁′ ismade to be equal to either β₁′ or β_(m−1)′ in the case where m is 3.Here, in spite of the expression “made to be equal”, a deviation at alevel of ±10% is allowable.

Thus, for an even number length mark, a recording pulse row 303 shown bya dotted line in FIG. 3(b) is obtained, and for an odd number lengthmark, a recording pulse row 307 shown by a dotted line in FIG. 3(c) isobtained.

Further, when m=1 (n=3), irradiation with a recording laser beamcomprising a pair of a writing power irradiation section α₁′T and a biaspower irradiation section β₁′T is carried out. In such a case, it ispreferred that α₁′ is made to be larger by from about 0.1 to 1.5 thanα₁′ in the case where m is at least 2, and β₁′ is made to be smallerthan β₁′ and to be the same as or larger than β_(m) and β_(m)′ in thecase where m is at least 2. Further, the range of β₁′ is preferably from0 to 2.

FIG. 16 is a graph showing one embodiment of the relation of therespective recording pulses in a case where the pulse-dividing methodsaccording to the above-mentioned recording methods DVD1-2 and 2-2 are tobe carried out. In FIG. 16(b), the time widths of recording pulses andoff-pulses to form mark lengths 2 mT should formally be represented byα₁T, β₁T, αcT, . . . α_(m)T, β_(m)T, but for the sake of simple clearrepresentation of the graph, in FIG. 16(b), they are simply representedby α_(i), β₁, αc, . . . α_(m), i.e. the indication of the referenceclock period T is omitted. The same applies also to FIG. 16(c).

As shown in FIG. 16, consideration is given whether the value which n innT mark can take, is an odd number or an even number. Correction of marklength difference 1T between an even number length mark and an oddnumber length mark for the same division number m is divided andallocated to a recording pulse periodic section (β_(m−1)+α_(m))T secondfrom the last and the last off-pulse β_(m)T. Namely, the correction ofmark length 1T is carried out by adjustment of off-pulse lengthsβ_(m−1)T and β_(m)T, and pulse α_(m)T of the last recording pulsesection.

As compared with the recording method shown in FIG. 3 (recording methodsDVD1-1, 2-1), in this recording method, recording pulses and off-pulsesto be changed as between even number and odd number marks, areconcentrated at the rear end portion of a mark, whereby there is notonly a merit in that the rear end jitter of a record mark can easily becontrolled, but also a merit in that the design of an electronic circuit(integrated circuit) to control generation of laser beams (pulsed beams)for recording pulses and off-pulses of the recording pulse strategy canbe simplified. Further, there is a merit that the number of parametersto be variable is small.

In FIG. 16, 400 represents the reference clock of period T.

FIG. 16(a) shows a pulse waveform corresponding to a record mark havinga length of nT=2mT or nT=(2m+1)T, wherein symbol 401 corresponds to thelength of a record mark having a length of 2mT, and symbol 402corresponds to the length of a record mark having a length of (2m+1)T.In FIG. 16(a), a case where m=5, is shown.

In FIG. 16(b), 403 represents a waveform of divided recording pulses ina case where n=2m(=10). In FIG. 3(c), 406 represents a waveform ofdivided recording pulses in a case where n=2m+1(=11).

A value obtained by multiplying T_(d1) by T represents a delay time tothe forward end T₀ of nT mark, of α₁T and α₁′T and is usually constantirrespective of n. Further, usually, (T_(d1)+α₁)T=(T_(d1)+α₁′)T=2T tofacilitate synchronization of the record pulse-generating circuit, butfine adjustment at a level of ±0.5T is further allowable. Especially for3T, 4T and 5T marks, it is preferred to carry out such fine adjustmentof the delay time. The writing power level at recording pulse sectionsα_(i)T (i=1 to m) is constant at Pw; the bias power level at off-pulsesections β_(i)T (i=1 to m) is constant at Pb; and the laser beamirradiation power between marks i.e. at sections other than α_(i)T (i=1to m) and β_(i)T (i=1 to m), is erasing power Pe which is constant. Whenn is an even number, at sections 404, (β_(i−1)+α_(i))T=2T (i=2 to m)i.e. constant, provided that fine adjustment within a range of ±0.3T isallowable only with respect to (β₁+α₂)T and (β_(m−1)+α_(m))T. On theother hand, in a case where n is an odd number, at sections 407 in FIG.16, (β_(i−1)′+α_(i)′)T=2T (i=2 to m−1) i.e. constant. However,(β₁′+α₂′)T is made to be equal to (β₁+α₂)T.

In order to record two types of mark lengths where n=2m and 2m+1 withthe same division number, section (β_(m−1)+α_(m))T is increased orreduced by about 1T to adjust its length. Due to an influence of heatinterference, etc., such a value may not precisely be 1T, but willgenerally be within a range of from 0.5 to 1.2T. β_(m) and β_(m)′ takesubstantially the same values within a range of from 0 to 2 (inrecording method DVD2-2, β_(m)′=within 0 to 3). However, to correct theinfluence over the jitter at the rear end of a mark, β_(m) and β_(m)′are individually finely adjusted. Especially in recording method DVD2-2,β_(m)′=β_(m)+Δ_(m)′, i.e. Δ_(m)′ (=0 to 1) is added to β_(m).

Referring to FIG. 16, recording corresponding to the mark lengthdifference 1T between even number length mark nT=10T and odd numberlength mark nT=11T, is carried out by the following operation 3.

Operation 3: As shown at section 408 in FIG. 16, Δ_(mm)T is added tosection (β_(m−1)+α_(m))T to obtain (β_(m−1)′+α_(m)′)T. Here,Δ_(mm)=Δ_(m−1)+Δ_(m), and Δ_(mm) is divided into Δ_(m−1) and Δ_(m), sothat Δ_(m−1) added to β_(m−1), and Δ_(m) is added to Δ_(m). Further, inorder to correct the influence to the jitter at the rear end of a mark,β_(m) is changed to β_(m)′ by an addition of Δ_(m)′.

The foregoing operation is carried out when m is at least 3, and Δ_(mm)takes a value of from 0.5 to 1.2. With respect to Δ_(m−1) and Δ_(m),Δ_(m−1) may take a value of from 0 to 0.6 (from 0 to 0.7 in recordingmethod DVD2-2), and Δ_(m) may take a value of larger than 0 and at most0.6, depending upon how Δ_(mm) is divided and distributed. Δ_(m−1) maybe zero, Δ_(m) is made larger than 0 so that α_(m)≠α_(m)′. When Δ_(m) ismade larger than 0, the shape of the rear end of a record mark where nis an odd number among the same division number m, will be stabilized,whereby the jitter characteristics will be remarkably improved. Morepreferably, Δ_(m−1) and Δ_(m) are made to have substantially equalvalues. When Δ_(m−1) and Δ_(m) are made to be substantially equal, itwill be possible to simplify the design of an electronic circuit(integrated circuit) to control generation of pulsed beams, whilemaintaining good jitter characteristics.

Δ_(m)′ takes a value of from 0 to 1, more preferably a value of from 0to 0.6. Especially at a linear velocity lower than 4-times velocity, itis preferred to make Δ_(m)′ larger than in the case of 6-, 8-, 10- or12-times velocity. On the other hand, at 6-, 8-, 10- or 12-timesvelocity, it is preferred to make Δ_(m)′=0.

Now, with respect to recording method DVD1-2, cases where m is at least3, m=2 and m=1 will, respectively, be described. Recording method DVD2-2will be described later.

In recording method DVD1-2, when m is at least 3, α₁′=α₁ and β₁′=β₁, andα_(i) and α_(i)′ are constant as αc irrespective of i where i=2 to m−1.Further, α₁(=α₁′) takes a value within a range of from 0.7 to 1.4, andαc and α_(m) take a value within a range of from 0.7 to 1.2. Morepreferably, α₁(=α₁′), αc and α_(m) are within a range of from 0.7 to 1.

Further, when m is at least 3, α_(i)(=α₁′), β₁, αc, β_(m−1), Δ_(m−1),α_(m), Δ_(m), β_(m) and Δ_(m)′ are constant irrespective of m. At6-times velocity or 8-times velocity, it is preferred that αc=α_(i) (i=2to m) is firstly made to be 1, and then fine adjustment within a rangeof ±0.2 is further carried out. For α₁ and α_(m), firstly, the samevalue as αc is employed, and fine adjustment is carried out within arange of larger by about 0.3 at the maximum than αc. Δ_(m) and Δ_(m−1)take about 0.4 as the initial value, and fine adjustment is carried outto obtain the prescribed mark lengths. Further, β_(m)′ at section 410 isfirstly made to be equal to β_(m) at section 405, and thereafter, fineadjustment is carried out.

Here, when m=2, (β₁′+α₂′)T is made longer by about 1T than (β₁+α₂)T,since m−1=1, they may be deemed to be (β_(m−1)′+α_(m)′)T and(β_(m−1)+α_(m))T, respectively. And, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ andβ₂′ are made to be equal to α₁, α₁′, β₂, β₂′, α₃, α₃′, β₃ and β₃′ in thecase where m=3, respectively. However, when m=2, α₁, α₁′, β₁, β₁′, α₂,α₂′, β₂ and β₂′ may further be finely adjusted within a range of about±10%.

Thus, for an even number length mark, recording pulse train 402 shown bya dotted line in FIG. 16(b) is obtained, and for an odd number lengthmark, recording pulse train 406 shown by a dotted line in FIG. 16(c) isobtained.

Further, when m=1 (n=3), irradiation with a recording laser beamcomprising a pair of a writing power irradiation section α₁′T and a biaspower irradiation section β₁′T is carried out. In such a case, α₁′ ispreferably made to larger by from about 0.1 to 1.5 than α₁′ in the casewhere m is at least 2. Further, the range of β₁′ is preferably from 0 to2.

In recording method DVD2-1, an even number length mark and an odd numberlength mark are recorded by the same rule as in recording method DVD1-1,and in recording method DVD2-2, an even number length mark and an oddnumber length mark are recorded by the same rule as in recording methodDVD1-2, but α_(i) and α_(i)′ (i=1 to m) are made to be values smallerthan in recording at a linear velocity of from 6 to 12-times velocityand within a range of from 0.1 to 1. Consequently, β_(i) and β_(i)′ (i=1to m) are made to be values larger than in recording at a linearvelocity of 6-times velocity, 8-times velocity, 10-times velocity or12-times velocity. Further, in the case of recording method DVD2-2,especially Δ′_(m) is made to be variable within a range of from 0 to 1.Further, Δ_(m−1)+Δ_(m)+Δ_(m)′ is preferably made to be within a range offrom 0.5 to 1.5.

When α_(i) and α_(i)′ in the case where the maximum linear velocityV_(max) in recording method DVD1-1 or DVD1-2 is made to be 6, 8, 10 or12-times velocity, are represented by α_(i0) and α_(i0)′, if the samemedium is subjected to recording at 2-times velocity, 2.5-timesvelocity, 3-times velocity or 4-times velocity (i.e. linear velocity Vis any one of 2V₁, 2.5V₁, 3V₁ and 4V₁) by recording method DVD2-1 orrecording method DVD2-2, they are generally set to be α_(i)=η(V/V_(max))α_(i0), and α_(i)′=η(V/V_(max)) α_(i0)′, and thereafter, fine adjustmentwithin a range of about ±0.1, is carried out.

Here, η is a real number within a range of from 0.8 to 1.5.Particularly, a value within a range of from 1.0 to 1.3 is firstlyemployed, and thereafter, measurement is carried out by enlarging therange to be from 0.8 to 1.5.

Further, in recording method DVD2-1 or 2-2, an exceptional rule may beapplied when n=5.

Namely, in recording method DVD2-1, when m=2 (n=4, 5), α₁, α₁′, α₂, α₂′,β₂ and β₂′ are made to be equal to α₁, α₁′, α₃ (α_(m)), α₃′ (α_(m)′), β₃(β_(m)) and β₃′ (β_(m)′) in the case where m is 3, respectively, β₁ ismade to be equal to either β₁ or β₂ (β_(m−1)) in the case where m is 3,and β₁′ is made to be equal to either β₁′ or β₂′ (β_(m−1)′) in the casewhere m is 3. However, in spite of the expression “made to be equal”, adeviation at a level of ±10% is allowable. Further, with respect to α₂′and β₂′ when m=2, the value may further be changed within a range of±0.5.

Further, in recording method DVD2-2, when m=2 (n=4, 5), α₁, α₁′, β₁,β₁′, α₂, α₂′, β₂ and β₂′ are made to be equal to α₁, α₁′, β₂(β_(m−1)),β₂′(β_(m−1)′), α₃ (α_(m)), α₃′(α_(m)′), β₃ (β_(m)) and β₃′(β_(m)′) inthe case of m=3, respectively. However, in spite of the expression “madeto be equal”, a deviation at a level of ±10% is allowable. Further, β₁′in the case where n=3, is preferably made to be within a range of from 0to 3.

With respect to RW-DVD expected to be used at a velocity of up to6-times velocity, the recording characteristics are defined at 2-timesvelocity and 6-times velocity, or at 3-times velocity and 6-timesvelocity; with respect to RW-DVD expected to be used at a velocity of upto 8-times velocity, the recording characteristics at 2.5-times velocityand 8-times velocity, the recording characteristics at 3-times velocityand 8-times velocity, or the recording characteristics at 4-timesvelocity and 8-times velocity, are, respectively, defined; with respectto RW-DVD expected to be used at a velocity of up to 10-times velocity,the recoding characteristics at 4-times velocity and 10-times velocityare defined; and likewise, with respect to RW-DVD expected to be used upto 12-times velocity, the recording characteristics at 4-times velocityand 12-times velocity, or the recording characteristics at 6-timesvelocity and 12-times velocity, or the recording characteristics at4-times velocity and 8-times velocity, are, respectively, defined;whereby a medium suitable for the after-mentioned CAV recording system,P-CAV recording system or ZCLV recording system, can substantiallyunivocally be defined from the viewpoint of recording/retrievinginterchangeability among drives. In such a case, it is preferred that inrecording method DVD2-1 or 2-2 in the measurement of a low linearvelocity side, the values of α_(i), α_(i)′, β_(i) and β_(i)′ are set sothat they are generally proportional to the linear velocity as mentionedabove (α_(i)=η (V/V_(max)) α_(i0), α_(i)′=η (V/V_(max)) α_(i0)′),whereby the medium characteristics can better be defined.

Thus, to define the characteristics of a rewritable optical recordingmedium at a plurality of recording linear velocities within differentrecording velocity ranges wherein the ratio between the minimum linearvelocity and the maximum linear velocity becomes at least two times, isa preferred method also with a view to securing recording/retrievinginterchangeability of a medium from the viewpoint of recording drives.It is particularly preferred to use recording method DVD1-1 incombination with recording method DVD2-1, and to use recording methodDVD1-2 in combination with recording method DVD2-2.

Thus, in the case of defining a medium within a specific range, it isparticularly preferred to combine recording method DVD1-2 with recordingmethod DVD2-2 to define RW-DVD with the maximum linear velocity V_(max)of 6-times velocity, 8-times velocity, 10-times velocity or 12-timesvelocity.

Further, in a method for defining the medium characteristicscorresponding to such 6-times velocity, 8-times velocity, 10-timesvelocity or 12-times velocity, recording method DVD1-2may be furtherdefined to present the following recording method DVD1-3, whereby themedium characteristics can more specifically be defined. Thus, it ispreferred that interchangeability can be secured when such a medium issubjected to recording by a plurality of recording devices.

Recording Method DVD1-3:

For a mark length of m=at least 2, T_(d1)′=T_(d1)=2-αc, α_(i)′=α_(i)=αc(i=1 to m−1), β_(i)′=β_(i)=2−αc (i=1 to m−2), α_(m)=αc and β_(m−1)322−αc, being constant, and β_(m−1)′=1+Δ_(m0) (0<Δ_(m0)≦0.7), α₁′=1+Δ_(m0)(0<Δ_(m0)≦0.7) and β_(m)′=β_(m)+Δ_(m)′, and Δ_(m0), Δ_(m)′ and β_(m) areconstant irrespective of m. Here, when m=2, β₁, β₁′, α₂, α₂′, β₂ and β₂′are deemed to be β₂(β_(m−1)), β₂′(β_(m−1)), α₃ (α_(m)), α₃′(α_(m)′),β₃′(β₃m) and β₃′(β_(m)′) in the case where m=3. αc is from 0.7 to 1.2,more preferably from 0.7 to 1, particularly preferably from 0.9 to 1.

Here, it is particularly preferred to combine recording method DVD1-3(to be applied at one of 6, 8, 10 or 12-times velocity) with thefollowing recording method DVD2-3 (to be applied at one of 2, 2.5, 3, 4or 5-times velocity) to define phase-change type rewritable DVD to beused at the maximum linear velocity V_(max) of 6-times velocity, 8-timesvelocity, 10-times velocity or 12-times velocity.

Recording Method DVD2-3:

For a mark length of m=at least 2 (n=4), T_(d1)′+α₁′=T_(d1)+α₁=2,α_(i)=αc (i=1 to m), α_(i)′=αc (i=1 to m−1), wherein αc=0.1 to 1,β_(i−1)+α_(i)=2 (i=2 to m) and β_(i−1)′+α_(i)′=2 (i=2 to m−1), andβ_(m−1)′=β_(m−1)+Δ_(m0) (0<Δ_(m0)≦0.7), α_(m)′=α_(m)+Δ_(m0)(0<Δ_(m0)≦0.7) and β_(m)′=β_(m)+Δ_(m)′ (Δ_(m)′=0 to 1), and further,Δ_(m0), β_(m) and Δ_(m)′ are constant irrespective of m. Here, when m=2,β₁, α₂ and β₂ are deemed to be β₂(β_(m−1)), β₃(β_(m)) and α₃′(α_(m)′) inthe case of m=3, respectively.

Recording methods DVD1-3 and 2-3 are characterized in that when an oddnumber record mark is to be formed among an even number record mark andan odd number record mark having the same division number m, equal Δ_(m)(which is represented by Δ_(m0) in recording methods DVD1-3 and 2-3) isimparted to an off-pulse section (β_(m−1)′) immediately before the lastand to the last recording pulse section (α_(m)′). By imparting equalΔ_(m) (which is represented as Δ_(m0) in recording methods DVD1-3 and2-3), the design of an electronic circuit (integrated circuit) tocontrol generation of laser beams (pulsed beams) for recording pulsesand off-pulses of the recording pulse strategy for forming record marks,can be simplified, whereby it will be possible to reduce the costs forthe electronic circuit (integrated circuit).

It is particularly preferred to make Δ_(m) larger than 0 with a view tostabilizing the shape of the rear end portion of the record mark toimprove the jitter characteristics. Specifically, it is preferred thatΔ_(m0) is made to be Δ_(m0) larger than 0 in recording methods 1-3 and2-3, and Δ_(m0) is made to be within a range of 0<Δ_(m0)≦0.7. In orderto stabilize the shape of the rear end portion of the record mark, morepreferred is that Δ_(m0) is made to be within a range of 0<Δ_(m0)≦0.6.

Further, with a view to stabilizing the shape of the rear end portion ofa record mark where n is an odd number to improve the jittercharacteristics, Δ_(m)′ is preferably set to be within a range of0<Δ_(m)′≦1, more preferably 0<Δ_(m)′≦0.6, particularly preferably withina range of 0<Δ_(m)′≦0.5.

And, at each linear velocity, the optimum values of minimum parametersare determined in accordance with the procedure shown in FIG. 17. Thatis:

1) Provisional values Pw_(a), Pe_(a) and Pb_(a) are determined for Pw,Pe and Pb.

2) EFM+ signals composed solely of an even number mark and a spacelength (containing all of n=4, 6, 8, 10 and 14) are recorded byirradiating Pw_(a), Pe_(a) and Pb_(a). As αc and β_(m) are variable,such αc and β_(m) are determined so that each mark length and each spacelength can be retrieved to have the prescribed length at the time of1-time velocity retrieving within a range where m₁₄=0.55 to 0.8, and thejitter value will be at most 15%.

3) Then, EFM+ signals obtained by adding an odd number mark length andspace length (including all of n=5, 7, 9 and 11) other than n=3, to theabove-mentioned EFM+ signals composed solely of an even number lengthmark and space length, are recorded by irradiation with Pw_(a), Pe_(a)and Pb_(a). For αc and β_(m), the above values are employed, andΔ_(m0)=β_(m−1)=Δ_(m) and Δ_(m)′ are variable, and such values aredetermined so that at the time of retrieving at 1-time velocity, thejitter value will be at most 15%.

4) Finally, complete FEM+ signals having 3T mark and space added, arerecorded by irradiation with Pw_(a), Pe_(a) and Pb_(a). With respect tothe mark length of n=at least 2, the above-mentioned values of αc,β_(m), Δ_(m0)=Δ_(m−1)=Δ_(m) and Δ_(m)′ are employed. Only T_(d1)′, α₁′and β₁′ relating to n=3 are variable, and such values are determined sothat at the time of retrieving at 1-time velocity, the jitter value willbe at most 15%.

5) Pw_(a) and Pe_(a) are variable, and fine adjustment of Pw and Pe iscarried out so that primarily, the jitter or the error rate will beminimum within a range where m₁₄=0.55 to 0.8. If, in each step of theabove procedure, m₁₄=0.55 to 0.8, and the jitter of at most 15%, can notbe obtained, such a medium is regarded as not satisfying therequirements of the present invention.

Further, in FIG. 17, the Pe/Pw ratio and the initial value of Pw aredetermined as follows.

A repeating pattern (hereinafter referred to as 14T data) composedsolely of 14T mark length and space length, is recorded in an unrecordedstate groove with Pe=0 and only Pw being variable. In this state, Pwwhereby m₁₄ would be within a range of from 0.55 to 0.8, is determinedto obtain the initial value Pw_(a). If m₁₄ increases beyond the range offrom 0.55 to 0.8 when Pw is increased, a Pw value whereby m₁₄ would beabout 0.7, is taken as the initial value Pw_(a). Then, Pe is irradiatedin a direct current fashion to the 14T data signals recorded by suchPw_(a), to measure the decrease of the carrier level of the 14T datasignals by dB (decibel value). This operation is repeated whileincreasing Pe within a range of Pe/Pw_(a)=0.2 to 0.6, and the first Pewhereby the decrease of the carrier level exceeds 25 dB, is taken as theinitial value Pe_(a) of Pe. As the initial value Pb_(a) of Pb, a powerequivalent to a retrieving laser beam power at a level where servo willbe stabilized at the time of retrieving with a power of 0<Pb_(a)<1 mW,is selected.

Further, in this specification, “overwriting” usually means to overwritenew data without returning once-recorded data to a uniform unrecorded orerased state by a certain specific treatment. However, in the presentinvention, also a case where recording is carried out in an initialuniform non-recorded or erased state is regarded as overwriting. Forexample, “overwriting ten times” in the case of evaluating thecharacteristics of an optical recording medium by means of the aboverecording method DVD1-1, 1-2, 2-1 or 2-2, means to carry out the firstrecording (overwriting first time) in the initial crystalline state andthen carry out overwriting 9 times. The same applies in the followingdescription.

Further, the definition of “α_(i)+β_(i−1)=2” in recording methodsDVD1-1, 1-2, 2-1 and 2-2, means that (α_(i)+β_(i−1)) is a time lengthtwice the reference clock period T and may contain an error at a levelof a fluctuation which inevitably results from the circuit design.Specifically, a difference at a level of 0.1T is regarded to besubstantially equal. Likewise, in the above description, for example, ina case where a specific α_(i) is made to be “constant” or “equal” toanother α_(i) or α_(i)′, inevitable fluctuation in practicing anelectronic circuit, is allowable.

Furthermore, even if the wavelength of the recording laser beam inrecording methods DVD1-1, 1-2, 2-1 and 2-2 is fluctuated within a rangeof from about 775 to 795 nm, such will not be a serious problem, sincewith a phase-change medium, the wavelength dependency within such awavelength range is very small.

2. Regarding the Recording Layer of the Medium

With the rewritable optical recording medium of the present invention,it is important to satisfy both erasing of amorphous marks in a shorttime by high speed crystallization and archival stability of amorphousmarks. Further, it is preferred to satisfy high modulation and at thesame time to satisfy the reflectivity and other is servo signalcharacteristics, etc., in the optical system used as the standard, inorder to secure retrieving interchangeability with the CD-ROM drive orDVD-ROM drive for retrieving only.

In order to satisfy both the high speed crystallization and the archivalstability, it becomes important firstly to select the material for thephase-change type recording layer to be formed on the substrate. In thepresent invention, it is important to increase the crystallization speedof the recording layer, which can be accomplished by adjusting thecomposition of the recording layer. In the present invention, in orderto increase the crystallization speed, it is preferred to employ acomposition containing Sb as the main component, for the phase-changetype recording layer. Here, in the present invention, “containing theprescribed composition or the prescribed element as the main component”means that in the entire layer containing the prescribed composition orthe prescribed element, the content of the prescribed composition or theprescribed element is at least 50 atomic %. The reason for containing Sbas the main component, is that the amorphous phase of Sb can becrystallized at a very high speed, whereby amorphous marks can becrystallized in a short time. Accordingly, erasing of record marks in anamorphous state will be facilitated. From this viewpoint, the content ofSb is preferably at least 60 atomic %, more preferably at least 70atomic %. However, on the other hand, rather than using Sb alone, it ispreferred to use together with Sb an additional element to facilitateformation of an amorphous phase and to increase the archival stabilityof the amorphous state. In order to facilitate formation of an amorphousphase of the phase-change type recording layer and to increase thearchival stability of the amorphous state, the content of the aboveadditional element is usually at least 1 atomic %, preferably at least 5atomic %, more preferably at least 10 atomic %, and on the other hand,it is usually at most 30 atomic %.

The above additional element to facilitate formation of an amorphousphase and to increase the archival stability of the amorphous state,also has an effect to increase the crystallization temperature. As suchan additional element, Ge, Te, In, Ga, Sn, Pb, Si, Ag, Cu, Au, a rareearth element, Ta, Nb, V, Hf, Zr, W, Mo, Cu, Cr, Co, nitrogen, oxygenand Se may, for example, be used. Among these additional elements,preferred is at least one member selected from the group consisting ofGe, Te, In, Ga and Sn, with a view to accelerating formation of anamorphous phase, improving the archival stability of the amorphous stateand increasing the crystallization temperature, and it is particularlypreferred to use Ge and/or Te.

As mentioned above, in the present invention, it is particularlypreferred to use Sb in combination with Ge and/or Te, as the materialfor the phase-change type recording layer. At the time of adding Geand/or Te to Sb, the content of Ge in the phase-change type recordinglayer is preferably from 1 atomic % to 30 atomic %, and the content ofTe is preferably from 0 atomic % to 30 atomic %. However, in a casewhere the main component of the phase-change type recording layer is Sb,the content of Sb will be at least 50 atomic %, and when Ge and Te areincorporated together with Sb to the phase-change type recording layer,the total amount of Ge and Te is preferably less than 50 atomic %, andfurther, when Te and Ge are compared, it is more preferred toincorporate Ge.

The content of Ge or Te in the phase-change type recording layer is morepreferably at most 3 atomic %, further preferably at most 5 atomic %. Ifthe content is within this range, an adequate effect to stabilizeamorphous marks will be obtained. On the other hand, the content of Geor Te in the phase-change type recording layer is more preferably atmost 25 atomic %, further preferably at most 20 atomic %. If the contentis within this range, it will be possible to excellently control thetendency such that the amorphous phase tends to be so stable that thecrystallization tends to be inversely slow, and accordingly it will bepossible to suppress a noise due to light scattering at crystal grainboundaries. Further, the total content of Ge and Te is preferably atmost 30 atomic %, more preferably at most 25 atomic %. If the totalcontent is within this range, it will be possible to excellently controlthe tendency such that the amorphous phase tends to be so stable thatthe crystallization will inversely be slow, and it will be possible tosuppress a noise due to light scattering at crystal grain boundaries.

Suitable compositions for the recording layer material to be used forthe phase-change type recording layer in the optical recording medium ofthe present invention may be classified into two types depending uponthe amount of Te contained in the phase-change type recording layer. Oneis a composition containing at least 10 atomic % of Te, and the other isa composition containing less than 10 atomic % of Te (inclusive of acase where no Te is contained).

As an example, the recording layer material is made to contain at leastabout 10 atomic % of Te and to have a compositional range wherein analloy containing Sb in excess of the Sb₇₀Te₃₀ eutectic composition, asthe main component Specifically, Sb/Te is made to be at lest 4.5,preferably at least 5.5 and on the other hand, at most 7.3.

As a specific example of the composition for the above recordingmaterial, a composition comprising Sb and Te, and further Ge, may bementioned. Namely, an alloy containing, as the main component, acomposition of Ge_(y)(Sb_(x)Te_(1-x))_(1-y) (where 0.01≦y≦0.06, and0.82≦x≦0.9) which comprises, as a matrix, a Sb₇₀Te₃₀ alloy having aSb₇₀Te₃₀ eutectic composition as the base and containing Sb in largeexcess and which further contains Ge, may be mentioned as a preferredcomposition for the above recording layer material. In the presentinvention, the composition is shown by the atomicity ratio. Thus, forexample, y=0.06 means 6 atomic %.

When an alloy (hereinafter referred to as a GeSbTe eutectic) of a GeSbTecomposition which comprises, as a base, a binary alloy containing Sb inexcess of Sb₇₀Te₃₀ and which further contains Ge, is used for thephase-change type recording layer, it is possible to obtain CD-RWoverwritable at a velocity of from 10- to 12-times velocity(JP-A-2001-229537). In such a case, the composition Sb_(x)Te_(1-x) ofthe SbTe alloy to be the matrix, is limited within a range of 0.7<x≦0.8.In this composition of the material, if the Sb/Te ratio is furtherincreased, the crystallization speed can further be increased.Accordingly, if attention is paid only to the erase ratio at 24-timesvelocity, the value can be increased as high as at least 20 dB byadjusting Sb/Te=at least 4.5 (0.82≦x). However, according to a studymade by the present inventors, it has been found that if the Sb/Te ratiois simply increased, the noise in the initial crystalline state(unrecorded state) after the production of an optical recording mediumcan not be lowered, and the jitter tends to be high, whereby it isdifficult to obtain an optical recording medium which satisfies therequirements for the quality or CD-RW signals such that mark and spacejitters in one-time velocity retrieving are at most 35 nsec.

Namely, with a composition which contains Te in an amount of at least 10atomic % and which has a Sb/Te ratio as high as at least 4.5, if the Gecontent exceeds 6 atomic %, the noise due to light scattering at crystalgrain boundaries tends to be very high. It is considered that if the Gecontent exceeds 6 atomic %, a GeTe phase will be formed, whereby apolycrystal structure showing remarkable mismatching at the grainboundaries is likely to be formed, and thus the above-mentioned noisedue to light scattering will be very high. Namely, with a compositionwhich contains at least 10 atomic % of Te and which has a Sb/Te ratio ashigh as at least 4.5, if the Ge content exceeds 6 atomic %, the noisewill be high already in an unrecorded crystalline state, whereby thejitter tends to be high, and it will be difficult to obtain goodrecording characteristics as CD-RW. Further, in a case where the atomicratios of Ge and Te are close to each other, an increase of the noisetends to result which is considered to be due to precipitation of a GeTephase. Accordingly, the atomic ratio of Ge to Te is preferably 1:atleast 3, more preferably 1:at least 4. On the other hand, if Te iscontained excessively relative to Ge, the archival stability ofamorphous marks tends to deteriorate. Accordingly, the atomic ratio ofGe to Te is preferably at most 1:20, more preferably at most 1:15.

Further, it has been also found that with a composition wherein theSb/Te ratio is simply increased, the crystallization speed tends to beso high that amorphous marks are likely to be recrystallized in a shorttime even in the vicinity of room temperature, whereby it is difficultto realize CD-RW having high reliability and having good overwritingcharacteristics.

Under the circumstances, the present inventors have conducted a furtherstudy and as a result, have found it possible to obtain a rewritableoptical recording medium overwritable at 24-times velocity whilemaintaining high quality of recording signals, by adjusting the Gecontent to be at most 6 atomic %, while increasing the Sb/Te ratio andfurther controlling the initial crystalline state after the productionof the optical recording medium.

With respect to the above-mentioned GeSbTe eutectic composition, detailsabout initializing conditions after forming the recording layer, whichare important to control the initial crystalline state after theproduction of the medium, will be described later, and firstly, theGeSbTe eutectic composition will be described.

A preferred composition for the GeSbTe eutectic composition isconsidered to be one containing, as the base, a ternary alloy having Geadded to a binary alloy containing Sb in excess of the SbTe eutecticcomposition, to improve the jitter and the archival stability ofamorphous marks. It is considered that in such a case, by the additionof Ge, the archival stability of amorphous marks can be increasedwithout impairing the high speed crystallization function by theexcessive Sb in the GeSbTe eutectic composition. As compared withanalogous Si, Sn or Pb, Ge has an effect to specifically improve thestability of amorphous marks. Further, Ge is considered to be an elementmost effective not only to increase the crystallization temperature butalso to increase the activation energy for crystallization.

The amount of Ge is preferably at least 0.01, particularly preferably atleast 0.02, as the value of y in Ge_(y)(Sb_(x)Te_(1-x))_(1-y). On theother hand, in such a SbTe eutectic composition containing a largecontent of Sb, if the amount of Ge is too much, an intermetalliccompound of GeTe or GeSbTe type will precipitate, and also a SbGe alloymay precipitate, and thus, it is considered that crystal grains havingdifferent optical constants tend to coexist in the phase-change typerecording layer. And, by the coexistence of such crystal grains, thenoise of the recording layer may increase, and the jitter may increase.Further, if Ge is added too much, the effect for the archival stabilityof amorphous marks will be saturated. Accordingly, the amount of Ge isusually at most 0.06, preferably at most 0.05, more preferably at most0.04, as the value of y in the above formula(Ge_(y)(Sb_(x)Te_(1-x))_(1-y))

On the other hand, if excessive Sb is too small, the recrystallizationspeed may be too low to carry out good overwriting at a high linearvelocity at a level of at least 20-times velocity. Accordingly,particularly for a medium overwritable at 24-times velocity, Sb/Te ispreferably made to be at least 5.5 (as the value of x inGe_(y)(Sb_(x)Te_(1-x))_(1-y), 0.85≦x, and on the other hand to be atmost 6.5 (as the value of x in Ge_(y)(Sb_(x)Te_(1-x))_(1-y), x≦0.87).

In the case of employing the GeSbTe eutectic composition, more preferredis a system having In and Ga further incorporated to the above GeSbTeeutectic composition. Namely, more preferred is to employ thephase-change type recording layer containing, as the main component, acomposition represented by M_(z)Ge_(y)(Sb_(x)Te_(1-x))_(1-y-z) (where0.01≦z≦0.1, 0.01≦y≦0.06, 0.82≦x≦0.9 and M is at least one elementselected from the group consisting of Ga and In).

The characteristics will be further improved by adding at least onemember selected from the above-mentioned group of elements representedby M=Ga and In. In and Ga are effective to reduce jitter. However, ifthe amount of element M is too much, segregation with time of a specificsubstance or segregation by repeated overwriting tends to take place.Accordingly, the amount of element M to be incorporated, is preferablyat most 0.1, more preferably at most 0.09, as the amount of z in theformula M_(z)Ge_(y)(Sb_(x)Te_(1-x))_(1-y-z). On the other hand, in orderto obtain the effect to reduce jitter by an addition of In or Ga, theabove value of z is preferably at least 0.01, more preferably at least0.03, further preferably at least 0.05.

As elements other than In and Ga which may be contained in the GeSbTeeutectic composition, nitrogen, oxygen and sulfur may be mentioned.These elements are effective for fine adjustment of opticalcharacteristics or to prevent segregation in repeated overwriting. Thecontent of nitrogen, oxygen and sulfur is more preferably at most 5atomic % based on the total amount of Sb, Te and Ge.

Further, Sn, Cu, Zr, Hf, V, Nb, Ta, Cr or Co may be contained in theGeSbTe eutectic composition. By an addition in a very small amount, suchan element increases the crystallization temperature without loweringthe crystal growth rate and is effective for further improvement of thearchival stability. However, if the amount of such an element is toomuch, segregation with time of a certain specific substance orsegregation by repeated overwriting is likely to take place.Accordingly, the amount is usually at least 1 atomic % and usually atmost 5 atomic %, preferably at most 3 atomic %. Once segregation takesplace, the stability of the amorphous phase which the recording layerinitially has, or the recrystallization speed of the like is likely tobe changed, whereby the overwriting characteristics may sometimesdeteriorate.

Here, the above-described recording layer composition being particularlypreferred as compared with other compositions, will be explained.

InGeSbTe alloys are disclosed also in JP-A-1-63195, JP-A-1-14083,JP-A-5-16528 and JP-A-9-294269, and in each disclosure, a composition inthe vicinity of a GeTe—Sb₂Te₃ pseudo binary alloy is regarded aspreferred.

The above-mentioned composition of the present invention is differentfrom such disclosures and is a composition which contains a SbTeeutectic composition as the main component and which contains Sb inlarge excess.

In the present invention, it is preferred that in the crystalline stateof the phase-change recording layer, the recording layer is formedmainly of the same crystalline phase. As a result, the noise decreases,the storage stability will be improved, and it is possible to obtain acharacteristic such that crystallization at a high velocity will beeasy.

In a case where a crystalline phase having a hexagonal structure such asSb₂Te₃, a crystalline phase which is a cubic crystal but has asubstantially different lattice constant such as Sb and further othercrystalline phases belonging to other space groups such as Sb₇Te,Sb₂Te₃, etc. are simultaneously present, large crystal grain boundarieshaving lattice mismatching will be formed, whereby it is likely thatperipheral shapes of marks tend to be irregular and optical noises willresult. Whereas, in a case where the recording layer is composed of thesame crystalline phase, such crystal grain boundaries will not beformed, whereby reduction of noises, improvement of the storagestability and high speed crystallization, etc. will be possible.

Here, in order to let the recording layer have the same crystallinephase, it becomes important to control the crystalline state after theproduction of the medium. This means that it is important to control theinitial crystallization conditions when the initial crystallizationoperation is carried out after forming the recording layer on thesubstrate. Details of such initial crystallization operation withrespect to the GeSbTe eutectic composition will be described later.

The recording layer containing Sb as the main component, to be used inthe present invention, exhibits a crystallization process consistingmainly of crystal growth. Namely, usually, the crystallization stepcomprises two steps i.e. formation of crystal nuclei which takes placeat a relatively low temperature range of at least the crystallizationtemperature and growth of crystal nuclei which proceeds at a relativelyhigh temperature range immediately below the melting point. However, therecording layer containing Sb as the main component to be used in thepresent invention, has such a characteristic that formation of crystalnuclei is little, and the crystal growth speed is extremely fast.

The optical recording medium to be used in the present invention isprepared by forming various layers such as the recording layer, etc.constituting the optical recording medium, followed by initialcrystallization of the recording layer to make the recording layer in anunrecorded or erased state having high reflectivity and thereby toobtain a final product. And, recording of information on the recordinglayer is carried out by irradiating the recording layer locally with afocused laser beam to melt and then quench the recording layer to formamorphous marks. On the other hand, erasing information from therecording layer is carried out by recrystallizing the thus formedamorphous marks to return the recording layer to a crystalline stateagain.

Here, such erasing (recrystallization) is accomplished by using theperipheral crystalline phase as crystal nuclei and by filling theamorphous portions with crystal growth from the peripheral portions ofamorphous marks. Accordingly, contribution of formation of crystalnuclei in the interior of amorphous marks, is little, and contributionof crystal growth from the peripheral crystalline portions, whichproceeds at a high temperature immediately below the melting point, isgoverning. Such erasing in the optical medium consisting mainly of thecrystal growth from the peripheral crystalline portions, of coursedepends on the size of the amorphous marks (see e.g. G. F Zohu et. al.,Proc. SPIE, Vol. 4090 (2000), p. 108). Especially in mark lengthmodulation recording on CD or DVD, slender marks are formed along theadvancing direction of the focused laser beam for recording/retrieving,and the above erasing depends on the mark width in the transversedirection to the advancing direction. Namely, as the mark width iswider, it takes more time in erasing such marks.

Accordingly, there is a situation such that with CD-RW or RW-DVD with arelatively low recording density, the size of amorphous marks tends tobe large, whereby high velocity erasing is difficult, and high velocityoverwriting is difficult, as compared with a high density mark lengthmodulation recording by an optical system (hereinafter referred to as ablue recording system) having a wavelength λ=about 400 nm and NA of afocusing object lens for a focused laser beam=about 0.85, for whichdevelopment has just recently been started.

According to a study made by the present inventors, it has been foundthat especially with recording layer compositions having the same Sb/Teratio, the square root of the diameter of the focused laser beamgenerally determined by λ/NA is inversely proportional to the upperlimit of the overwritable linear velocity. For example, with respect tothe above-mentioned blue recording system, a recording layeroverwritable at about 20 m/s has already been reported by the presentinventors, wherein a Sb/Te eutectic recording layer having Ge added, isused (Horie et al., Proc. SPIE, Vol. 4342 (2001), p. 76). With the bluerecording system, overwriting at 20 m/s can be accomplished even whenthe Sb/Te ratio is generally about 4. However, with the RW-DVD system(λ=660 nm, NA=0.65), overwriting is possible only to a level of about 14m/s. Further, with the CD-RW system (λ=780 nm, NA=0.5), overwriting ispossible only at a level of 11 m/s. Namely, even if a recording layeroverwritable at a high linear velocity of more than about 20 m/s withthe blue recording system, is simply applied, no satisfactoryoverwriting can be accomplished at from 18 to 20-times velocity withCD-RW or at about 5-times velocity with RW-DVD. Further, the bluerecording system is applicable even to a recording layer whereby theinfluence of a noise due to crystal grains is low, and the Sb/Te ratiois high and the crystal grain boundary noise is relatively high.However, in an application to CD-RW or RW-DVD, the influence of a noisedue to crystal grain boundaries as the Sb/Te ratio becomes high, can notbe neglected.

Accordingly, in order to apply the SbTe eutectic material to RW-DVD orCD-RW, it is necessary to increase Sb/Te more and to bring it to a levelof at least 4.5. On the other hand, the Sb/Te ratio may not simply beincreased, and it is necessary to take a measure to lower the noise dueto crystal grain boundaries by improving the above-mentioned compositionrange and the after-mentioned initialization method. Further, it isnecessary to pay more attention also to the stability of amorphous marksin the vicinity of room temperature. Of course, it is necessary to carryout a substantial review taking into consideration the modulation andR_(top), also with respect to the thickness, etc. of the protectivelayer, etc. as other constituting elements of the optical recordingmedium, to be used in the present invention.

The following may be mentioned as another suitable composition for therecording layer material to be used for the optical recording medium ofthe present invention, which can be classified by the amount of Tecontained in the phase-change type recording layer. Namely, thecomposition of the phase-change type recording layer is made to containTe in an amount of less than 10 atomic %, while using Sb as the maincomponent and further made to contain Ge as an essential component. Withsuch a composition, overwriting at 32-times velocity of CD-RW will bepossible.

As a specific example of the above-mentioned composition for thephase-change type recording layer, an alloy (in this specification, thismay sometimes be referred to as a GeSb type eutectic alloy) comprisingas the main component an eutectic alloy having a composition close toGe₁₀Sb₉₀ and containing less than 10 atomic % of Te, may preferably bementioned. The composition in which the amount of Te is less than 10atomic %, is not a SbTe eutectic, but tends to have a nature as a GeSbtype eutectic alloy containing GeSb eutectic as the base. With such aGeSb type eutectic alloy, even if the Ge content is high at a level of10 atomic %, the crystal grain size in the polycrystalline state afterthe initial crystallization is relatively fine, whereby the crystallinestate is likely to be a single phase, whereby the noise is low. In theGeSb type eutectic alloy, Te is added merely as an additive and is notan essential element.

With the GeSb type eutectic alloy, the crystallization speed can beincreased by adjusting the Sb/Ge ratio to be relatively high, wherebyrecrystallization of amorphous marks by recrystallization is possible.According to a study made by the present inventors, it has been foundthat with an optical recording medium using such a GeSb type eutecticalloy as the phase-change recording material, the amorphous marks aremore stable than the above-mentioned GeSbTe eutectic system, even thoughhigh velocity crystallization is possible to such an extent that withCD-RW, an erase ratio of 25 dB can be accomplished at 32-times velocity.Further, it has been found that an optical recording medium employingsuch a GeSb type eutectic alloy as the phase-change recording material,has a characteristic such that no increase in the noise is observed asobserved when the Sb/Te ratio is increased to enable erasing at 24-timesvelocity or even at 32-times velocity with the above-mentioned GeSbTeeutectic system, and thus recording at a low noise will be possible.

In fact, a recording layer in a crystalline state of an unrecorded orerased state, was peeled and inspected by a transmission electronmicroscope, whereby it was found that in the alloy recording layercontaining the GeSb eutectic crystals as the base, the crystal grainsize was smaller than in an alloy recording layer containing the SbTeeutectic crystals as the base, and thus, this is effective for loweringthe noises attributable to light scattering due to the anisotropy ofcrystals or crystal grain boundaries.

Here, in a case where such a GeSb type eutectic alloy is used as themain component, the content of Ge is preferably made to be at least 1atomic % and at most 30 atomic %.

As a preferred composition for such a GeSb type eutectic alloy,Te_(γ)M1_(β)(Ge_(α)Sb_(1-α))_(1-β-γ)(where 0.01≦α≦0.3, 0≦β≦0.3, 0≦γ<0.1,2≦β/γ, 0<β+γ≦0.4, and M1 is one member selected from the groupconsisting of In, Ga and Sn) may be mentioned. By adding In, Ga or Sn tothe GeSb binary eutectic alloy, it is possible to make distinct theeffect for increasing the difference in optical characteristics betweenthe crystalline state and the amorphous state and thereby to obtain highmodulation with interchangeable media of CD-RW and RW-DVD.

In the above TeM1GeSb type composition, Ge serves to facilitateformation of an amorphous phase and to increase the storage stability ofamorphous record marks. Accordingly, a representing the content of Ge ismade to be usually at least 0.01, preferably at least 0.03, morepreferably at least 0.05. On the other hand, if the content of Gebecomes large, the crystallization speed decreases. Accordingly, inorder to secure erasing performance in overwriting at a high velocity ofat least 20 m/s, α is made to be usually at most 0.3, preferably at most0.2.

Further, in the above TeM1GeSb type composition, elements M1 is onemember selected from the group consisting of In, Ga and Sn.

By using In or Ga as element M1, the jitter in ultra high velocityrecording will be improved, and the optical contrast may be increased.For this purpose, β representing the content of In and/or Ga is made tobe usually at least 0, preferably at least 0.01, more preferably atleast 0.05. However, if In or Ga is too much, separately from thecrystal phase to be used for an erased state, other crystal phases ofIn—Sb type or Ga—Sb type having a very low reflectivity, will be formed.Especially during the storage for a long time, such crystal phases willprecipitate, and R_(top) will decrease. Accordingly, β is made to beusually at most 0.3, preferably at most 0.2, more preferably at most0.15. Further, when In and Ga are compared, In is better in realizinglower jitter, and it is therefore preferred to use In for the above M1.

On the other hand, by using Sn as element M1, jitter in ultra highvelocity recording can be reduced, and the optical contrast (thedifference in reflectivity between the crystalline state and theamorphous state) can be made large. Accordingly, β representing thecontent of Sn is made to be usually at least 0, preferably at least0.01, more preferably at least 0.05. However, if Sn is too much, theamorphous phase immediately after recording is likely to change toanother amorphous phase having a low reflectivity. Especially during thestorage for a long time, such a stabilized amorphous phase willprecipitate to lower the erasing performance. Accordingly, β is made tobe usually at most 0.3, preferably at most 0.25, more preferably at most0.2, further preferably at most 0.15, particularly preferably at most0.12.

As element M1, a plurality of elements among In, Ga and Sn may be used.In a case where a plurality of elements are used as element M1, it ispreferred that In and Sn are contained with a view to enlarging themodulation. In a case where In and Sn are contained, the total contentof such elements is made to be usually at least 1 atomic %, preferablyat least 5 atomic % and usually at most 40 atomic %, preferably at most30 atomic %, more preferably at most 25 atomic %.

In the above TeM1GeSb type composition, by incorporating Te, it ispossible to improve the archival change of the erase ratio in ultra highvelocity recording. For this purpose, γ representing the content of Teis made to be usually at least 0, preferably at least 0.01, morepreferably at least 0.02, further preferably at least 0.03, particularlypreferably at least 0.05. However, if Te is too much, the noises maysometimes become high. Accordingly, γ is made to be usually less than0.1, preferably at most 0.09, more preferably at most 0.08, morepreferably at most 0.07.

Further, in a case where in the above TeM1GeSb type composition, Te andelement M1 are incorporated, it is effective to control the totalcontent thereof. Accordingly, β+γ representing the contents of Te andelement M1, is made to be usually larger than 0, preferably at least0.01, more preferably at least 0.05. By making β+γ within the aboverange, the effect of simultaneously incorporating Te and element M1 willbe excellently provided. On the other hand, in order to excellentlyprovide the effect of using the GeSb type eutectic alloy as the maincomponent, β+γ is made to be usually at most 0.4, preferably at most0.35, more preferably at most 0.3. On the other hand, β/γ representingthe atomicity ratio of element M1 to Te is preferably made to be atleast 2. By incorporating Te, the optical constant tends to decrease,and accordingly, in a case where Te is incorporated, it is preferred toslightly increase the content of element M1 (to slightly increase β).

Elements which may be added to the above TeM1GeSb type compositioninclude, for example, Au, Ag, Pd, Pt, Si, Pb, Bi, Ta, Nb, V, Mo, rareearth elements, N and O, which may be used for e.g. fine adjustment ofthe optical characteristics or the crystallization speed. However, theiramount is about 10 atomic % at the maximum.

In the foregoing, one of the most preferred compositions is acomposition containing as the main component an alloy system ofIn_(p)Sn_(q)Te_(r)Ge_(s)Sb_(t) (0≦p≦0.3, 0≦q≦0.3, 0<p+q≦0.3, 0≦r<0.1,0<s≦0.2, 0.5≦t≦0.9, and p+q+r+s+t=1). In a case where Te and In and/orSn are used in combination, it is preferred to make (p+q)/r≦2.

By employing the above composition, in the GeSb eutectic system, anincrease of modulation can be accomplished by incorporating In or Sn,and reduction of jitter can also be accomplished. And, by incorporatingTe, the archival stability of the erasing ability can be improved.Further, in the above composition, appearance of the crystalline phaseattributable to any additional element can be suppressed, and there willbe a merit in that single phase polycrystals composed substantially ofhexagonal system crystals of Sb as the base, will be constantly formed.

In a case where either the above GeSbTe eutectic composition or the GeSbtype eutectic composition is employed for the recording layer, it ispreferred that the crystalline phase of the recording layer is formedmainly of the same crystalline phase. Such a form of the crystallinephase depends substantially on the initialization method for therecording layer. Namely, in order to form the preferred crystallinephase in the present invention, it is preferred to arrange theinitialization method for the recording layer as follows.

The recording layer is formed usually by a physical vapor depositionmethod in vacuum such as a sputtering method. However, in anas-deposited state immediately after the deposition, it is usuallyamorphous, and therefore, it is usually crystallized to form anunrecorded or erased state. This operation is referred to asinitialization (in this specification, the initialization may sometimesbe referred to as “initial crystallization operation” or “initialcrystallization”). As the initialization operation, a method such asoven is annealing in a solid phase at a temperature of at least thecrystallization temperature (usually from 150 to 300° C.) and at mostthe melting point, annealing under irradiation with a light energy ofe.g. a laser beam or a flash lamp beam, or melt initialization, may bementioned. However, in order to obtain a recording layer in theabove-mentioned preferred crystalline state, it is preferred to employmelt initialization. In the case of annealing in a solid phase, there isa time until the thermal equilibrium is reached, whereby othercrystalline phases are likely to be formed. Whereas, in a case wheremelt initialization is employed crystal nuclei can more readily beformed than in the case of the solid phase, and the time until thethermal equilibrium is reached can be shortened, whereby there is anadvantage such that a single crystalline phase is likely to be readilyformed.

In the melt initialization, the recording layer may be melted anddirectly recrystallized during resolidification, or it may be onceformed into an amorphous state during resolidification and thensubjected to solid phase recrystallization in the vicinity of themelting point. In such a case, if the crystallization speed is too slow,there will be a time until the thermal equilibrium is reached, wherebyother crystalline phases are likely to be formed. Accordingly, it ispreferred to increase the cooling rate to some extent.

In the melt initialization, the time for maintaining the temperature ata level of at least the melting point is usually preferably at most 2μs, preferably at most 1 μs. Further, for the melt initialization, it ispreferred to employ a laser beam. It is particularly preferred to carryout initialization by using an oval laser beam having its minor axissubstantially in parallel with the scanning direction (hereinafter, thisinitialization method may sometimes be referred to as “bulk erasing”).In such a case, the length of the major axis is usually from 10 to 1000μm, and the length of the minor axis is usually from 0.1 to 10 μm. Here,the lengths of the major axis and the minor axis of the beam are definedfrom the half value width in a case where the light energy intensitydistribution within the beam is measured. In a case where scanning iscarried out at a speed higher than the overwritable maximum practicallinear speed of the phase-change medium to be used, there may be a casewhere a region once melted in the initialization operation turns into anamorphous phase. Accordingly, it is preferred to carry out the operationat a linear velocity of not higher than the overwritable maximumpractical linear velocity. Here, the maximum practical linear velocityitself is determined as the upper limit of the recording linear velocitywhere the erase ratio exceeds 20 dB when the erase ratio is measured byoverwriting at that linear velocity. As the laser beam source, varioustypes may be used including, for example, a semiconductor laser and agas laser. The power of the laser beam is usually from about 100 mW to5W.

Now, a preferred scanning speed for a recording layer employing theGeSbTe eutectic composition will be described.

With a GeSbTe eutectic composition having a Sb/Te ratio of at most 4,whereby from 10 to 12-times velocity is the upper limit of theoverwritable maximum practical linear velocity, as disclosed inJP-A-2001-229537, a preferred scanning speed is from about 3 to 10 m/s.Further, also with a GeSbTe eutectic composition expected foroverwriting at about 16-times velocity, as disclosed inJP-A-2001-331936, a preferred scanning speed is from about 3 to 10 m/s.Thus, there has been a tendency that the scanning speed forinitialization is increased as the practical overwriting linear velocityincreases.

Whereas, it has been found that as in the present invention, with aGeSbTe eutectic composition wherein the Sb/Te ratio is made to be veryhigh at a level of at least 4.5, excellent initial crystallization canbe carried out at a rather low linear velocity of from 0.1 to 3 m/s,particularly preferably at a low linear velocity of about 2 m/s.

On the other hand, with a recording layer of a GeSb type eutecticcomposition (GeSb type eutectic alloy), it is advisable to initialize byscanning at a high linear velocity, and initialization may be carriedout usually at from 10 to 20 m/s.

When initialization by bulk erasing is to be carried out by using, forexample, a disk-form recording medium, the minor axis direction of anoval beam is brought substantially into line with the circumferentialdirection, and by rotating the disk, scanning is carried out in theminor axis direction, while moving the beam in the major axis (radial)direction every full circle (one rotation), whereby initialization canbe carried out over the entire surface. The moving distance in theradial direction per one rotation is preferably set to be shorter thanthe major axis of the beam, so that the same radial region will beirradiated a plurality of times with the laser beam. As a result,initialization can certainly be carried out, and at the same time, it ispossible to avoid non-uniformity of the initial crystallization stateattributable to the energy distribution (usually from 10 to 20%) in theradial direction of the beam. On the other hand, if the moving distanceis too short, the above-mentioned other undesirable crystalline phasestend to be formed. Accordingly, the moving distance in the radialdirection per one rotation is usually set to be at least ½ of the majoraxis of the beam. Whether or not melt recrystallization has beenproperly done, can be judged by determining whether or not thereflectivity R1 in the erased state (crystalline state) afteroverwriting amorphous marks a plurality of times with a practicalrecording beam of about 1 μm, is substantially equal to the reflectivityR2 in the unrecorded state after the initial crystallization. Here, in acase where a signal pattern such that an amorphous mark isintermittently recorded, is employed, the measurement of R1 is usuallycarried out after overwriting a plurality of times at a level of from 5to 100 times. In such a manner, an influence of the reflectivity atspaces between marks which may remain in an unrecorded state ifrecording is carried out only once, can be removed.

The above erased state for the measurement of reflectivity R1 may alsobe obtained by irradiating the writing power in a direct current fashionto melt the recording layer, followed by resolidification, withoutnecessarily modulating the focused recording laser beam in accordancewith a practical recording pulse-generating method.

In the present invention, it is preferred that the value of thefollowing formula (F1) defined by R1 and R2 would become at most 10(%),particularly preferably at most 5(%).2|R1−R2|/(R1+R2)×100(%)  (F1)

For example, with a phase-change medium having R1 of about 17%, R2maygenerally be within a range of from 16 to 18%.

And, in order to satisfy the above (F1), it is preferred to give a heathistory substantially equal to the practical recording conditions, bythe initial crystallization. Further, an alloy recording layer(crystalline state) comprising, as the main component, Sb in anunrecorded state after such initialization or in an erased state afteroverwriting thereon a plurality of times, was peeled, and the recordinglayer was inspected by a transmission electron microscope, whereby itwas found that a single phase was formed wherein only a crystallinephase close to pure hexagonal crystals of Sb was observed, and thecrystal grains were aligned in a specific direction with respect to therecording in-plane direction.

3. Regarding the Layer Structure of the Medium

Now, the layer structure of the medium to be used in the presentinvention and layers other than the recording layer will be described.It is important to control the layer structure and the compositions oflayers other than the recording layer in order to satisfy both highspeed crystallization of the recording layer and the archival stabilityof record marks and to maintain retrieving interchangeability with CD orDVD while bringing the optical characteristics of the medium within thespecific ranges.

For the substrate of the medium of the present invention, a resin suchas polycarbonate, acryl or polyolefin, or glass, may be employed. Amongthem, a polycarbonate resin is most preferred, since a polycarbonate ismost commonly used for CD or DVD and is inexpensive. Further, in a casewhere a converged light beam enters from the substrate side, thesubstrate is preferably transparent. The thickness of the substrate isusually at least 0.1 mm, preferably at least 0.3 mm and on the otherhand, usually at most 20 mm, preferably at most 15 mm. Usually, in thecase of CD, the thickness is about 1.2 mm, and in the case of DVD, thethickness is about 0.6 mm.

In the case of DVD, a phase-change type recording layer is formed onsuch a substrate via prescribed layers such as a reflective layer and aprotective layer, and further, a substrate is again formed on thisphase-change type recording layer via a prescribed layer such as aprotective layer. Namely, in DVD, a structure is adopted wherein thephase-change type recording layer is sandwiched between two substrates.

The recording layer preferably has both sides covered with protectivelayers to prevent deformation due to a high temperature at the time ofrecording (for the convenience of description, the protective layer onthe incident light side of the recording layer may sometimes be referredto as a lower protective layer, and the protective layer on the oppositeside may sometimes be referred to as the upper protective layer).

In order to maintain the interchangeability with the current CD or DVDsystem, a desired layer structure of the medium is such that on asubstrate, a lower protective layer, a recording layer, an upperprotective layer and a reflective layer are formed. In this case, thesurface on the opposite side to the substrate may be coated with a resin(protective coating) curable by ultraviolet rays or heat.

The recording layer, the protective layer and the reflective layer canbe formed by sputtering. In such a case, it is preferred to carry outdeposition by sputtering in an in-line apparatus having a recordinglayer target, a protective layer target and, if necessary, a reflectivelayer material target provided in the same vacuum chamber, with a viewto preventing oxidation or contamination among the respective layers ofthe recording layer, the protective layer and the reflective layer.

The material to be used for the protective layer is determined takinginto consideration the refractive index, the thermal conductivity, thechemical stability, the mechanical strength, the adhesive property, etc.Usually, an oxide, sulfide, nitride or carbide of a metal orsemiconductor, having high transparency and high melting point, or afluoride of Ca, Mg, Li or the like, may be employed. Such an oxide,sulfide, nitride or fluoride may not necessarily take a stoichiometricalcomposition, and the composition may be controlled to adjust therefractive index, etc., and it is effective to use them as mixed.

When repeated recording characteristics are taken into consideration, amixture of dielectrics is preferred. More specifically, a mixture of ZnSand ZnO, or a rare earth sulfide and a heat resistant compound such asan oxide, nitride or carbide, may be mentioned. The film density of suchprotective layers is preferably at least 80% of the bulk state, from theviewpoint of the mechanical strength.

In the present invention, the thermal conductivity of the protectivelayer, particularly of the upper protective layer, is preferably assmall as possible. Specifically, it is preferred to use one having athermal conductivity of at most 1 J/(m·k·s). As such a material, ZnS ora mixture containing ZnS in an amount of at least 50 mol %, may bementioned.

The thickness of the lower protective layer is usually at least 30 nm,preferably at least 50 nm, more preferably at least 60 nm, particularlypreferably at least 80 nm. In order to suppress deformation of thesubstrate due to heat damage at the time of repeated overwriting, alayer thickness of some extent is necessary, and if the thickness of thelower protective layer is too thin, the repeated overwriting durabilitytends to abruptly deteriorate. Particularly, at an initial stage wherethe repeated number of times is less than a few hundred times, jittertends to abruptly increase. With respect to CD-RW, the thickness of thelower protective layer is particularly preferably made to be at least 80nm.

Deterioration of jitter at the initial stage of repetition dependslargely on the thickness of the lower protective layer. According to anobservation by an atomic force microscope (AFM) conducted by the presentinventors, it has been found that this initial deterioration is due to adeformation such that the substrate surface caves in by about from 2 to3 nm. To suppress such a substrate deformation, the protective layer isrequired to have a sufficient thickness to provide a heat insulatingeffect not to conduct the heat generation of the recording layer to thesubstrate and to mechanically suppress the deformation, and for thatpurpose, the above-mentioned thickness is preferred.

Further, by controlling the thickness of the lower protective layer, thereflectivity R_(top) can be adjusted to the prescribed range.

Namely, with a protective layer made of a dielectric material having arefractive index of from about 2.0 to 2.3 which is commonly employed forCD-RW employing a laser having a wavelength of about 780 nm, it is usualthat if the thickness of the lower protective layer is made to be from60 to 80 nm, the reflectivity R_(top) will be minimum, and if thethickness of the lower protective layer is made to be 0 and about 150nm, the reflectivity R_(top) will be maximum. Namely, along with thechange in the thickness of the lower protective layer, the reflectivityshows a periodic change taking the maximum and the minimum. Accordingly,it is optically meaningless to increase the thickness so much, and suchwill increase the material cost or may bring about a phenomenon (groovecoverage phenomenon) wherein the groove formed on the substrate isembedded by the deposition of the thick film. Accordingly, in order toadjust R_(top) to be from 15 to 25%, the lower protective layer isusually made to be at most 120 nm, preferably at most 100 nm, morepreferably at most 90 nm.

On the other hand, with a protective layer made of a dielectric materialhaving a refractive index of from about 2.0 to 2.3 which is commonlyused in RW-DVD employing a laser having a wavelength of about 660 nm, itis usual that if the thickness of the lower protective layer is made tobe from 50 to 70 nm, the reflectivity R_(top) will be minimum, and ifthe thickness of the lower protective layer is made to be 0 or about 130nm, the reflectivity R_(top) will be maximum. Accordingly, from the sameviewpoint as for CD-RW, the lower protective layer is made to be usuallyat most 100 nm, preferably at most 90 nm.

On the other hand, the thickness of the upper protective layer isusually at least 10 nm. In CD-RW, the thickness of the upper protectivelayer is preferably at least 20 nm, more preferably at least 25 nm. InRW-DVD, the thickness of the upper protective layer is preferably atleast 15 nm, more preferably at least 18 nm.

The upper protective layer primarily prevents the mutual diffusion ofthe recording layer and the reflective layer. If the upper protectivelayer is too thin, the upper protective layer is likely to be broken bye.g. deformation at the time of melting of the recording layer, or heatdissipation at the recoding layer tends to be too large, whereby thepower required for recording tends to be unnecessarily large (therecording sensitivity deteriorates). Especially when it is desired tocarry out recording at a high velocity as in the present invention,deterioration of the recording sensitivity is undesirable.

On the other hand, if the upper protective layer is too thick, thetemperature distribution within the protective layer tends to be sharp,whereby deformation of the protective layer itself tends to be large,and such deformation will be accumulated by overwriting and thus maybring about deformation of the medium. From such a viewpoint, in CD-RW,the thickness of the upper protective layer is made to be usually atmost 60 nm, preferably at most 55 nm, more preferably at most 35 nm. Onthe other hand, in RW-DVD, the thickness of the upper protective layeris made to be usually at most 35 nm, preferably at most 30 nm.

Now, the recording layer will be described.

In CD-RW, thickness of the recording layer is made to be usually atleast 10 nm, preferably at least 15 nm. On the other hand, in RW-DVD,the thickness of the recording layer is made to be usually at least 8nm, preferably at least 15 nm. If the thickness of the recording layeris too thin, no adequate optical contrast tends to be obtainable, andthe crystallization speed tends to be slow. Further, it tends to bedifficult to erase the record in a short time.

On the other hand, the thickness of the recording layer is made to beusually at most 40 nm. In CD-RW, the thickness of the recording layer ismade to be preferably at most 30 nm, more preferably at most 25 nm. Onthe other hand, in RW-DVD, the thickness of the recording layer is madeto be preferably at most 25 nm, more preferably at most 20nm. If thethickness of the recording layer is too thick, the optical contrasttends to be hardly obtainable, like in the case where the thickness ismade thin, and further, the thermal capacity of the recording layerincreases, whereby the recording sensitivity may sometimes deteriorate.Furthermore, the volume change of the recording layer accompanying thephase change, tends to be large as the recording layer becomes thick.Accordingly, if the recording layer is too thick, microscopicdeformation will be accumulated in e.g. the protective layers and thesubstrate surface at the time of repeated overwriting, which may bringabout an increase of noises.

The thicknesses of the recording layer and the protective layers areselected taking into consideration the interference effects attributableto the multilayer structure in addition to restrictions from theviewpoint of the mechanical strength and reliability (particularly therepeated overwriting durability), so that the efficiency for absorptionof the laser beam will be good, and the amplitude of recording signals,i.e. the contrast between the recorded state and the unrecorded state,will be large.

For a layer structure to balance all of these, firstly, the refractiveindex of the upper and lower protective layers is made to be from 2.0 to2.3. And, when the thickness of the lower protective layer isrepresented by d_(L), the thickness of the recording layer by d_(R) andthe thickness of the upper protective layer by d_(U), in CD-RW,15≦d_(R)≦25 nm, and 10≦d_(U)≦60 nm. Further, the value of d_(L) ispreferably controlled so that in the d_(L) dependency of the reflectedlight R_(top) against the crystalline state at the time of retrieving,d_(L) will be ∂R_(top)/∂d_(L)≧0 between the minimum value of R_(top) andthe next minimum value in the thickness direction within a range of from60 to 120 nm.

On the other hand, in RW-DVD, when the thickness of the lower protectivelayer is represented by d_(L), the thickness of the recording layer byd_(R) and the thickness of the upper protective layer by d_(U),10≦d_(R)≦20 nm, and 15≦d_(U)≦30 nm. Further, the value of d_(L) ispreferably controlled so that in the d_(L) dependency of the reflectedlight R_(top) against the crystalline state at the time of retrieving,d_(L) will be ∂R_(top)/∂d_(L)≧0 between the minimum value of R_(top) andthe next minimum value in the thickness direction within a range of from50 to 100 nm.

With the optical recording medium of the present invention, as comparedwith the conventional CD-RW medium where the maximum practical linearvelocity is 4-times velocity or 10-times velocity or the conventionalRW-DVD medium where the maximum practical linear velocity is up to2.4-times velocity, it is important to further increase the heatdissipation effect of the reflective layer. By adjusting thecharacteristics of the reflective layer and further combining it withthe above recording layer, recording at both high-linear velocity andlow-linear velocity will be more readily possible. Further, by using amaterial having a low thermal conductivity for the above protectivelayers, a larger effect can be obtained.

Formation of an amorphous phase and the recrystallization process, andthe relation between the heat dissipating effect of the reflective layerand the recording linear velocity, will be described with reference toFIG. 4.

In FIG. 4, the horizontal axis represents the recording linear velocity,and the left vertical axis represents the cooling rate when therecording layer is melted and resolidified, and if this cooling rate Ris larger than the critical cooling rate R_(c) determined by therecording layer material, the recording layer will be amorphous, andamorphous marks will be formed. In the left vertical axis in FIG. 4, anincrease of the crystallization speed of the recording layer means thatR_(c) will be large and moves upwards.

The relation between formation of an amorphous phase and the recordinglinear velocity in the case of realizing an optical recording mediumwherein the minimum linear velocity and the maximum linear velocity inrecording information on the optical recording medium are different atleast twice by a combination of any one of the above recording methodsCD1-1, 1-2 and 1-2 with any one of the above recording methods CD2-1,2-2 and 2-3 (for example, an optical recording medium to be used at theminimum linear velocity being 8-times velocity, 10-times velocity or12-times velocity of the reference linear velocity and at the maximumlinear velocity being 24-times velocity of the reference linearvelocity, or an optical recording medium to be used at the minimumlinear velocity being 8-times velocity, 10-times velocity, 12-timesvelocity or 16-times velocity of the reference linear velocity and atthe maximum linear velocity being 32-times velocity of the referencelinear velocity) will be described with reference to FIG. 4. Forexample, in a case where the minimum linear velocity is 8-times velocityof the reference linear velocity, and the maximum linear velocity is32-times velocity of the reference linear velocity, by using therecording layer composition and the layer structure of the opticalrecording medium of the present invention and/or the recording method ofthe present invention, it will be possible to make the cooling rate ofthe optical recording medium to be at least R_(c) at every linearvelocity as shown by curve d in FIG. 4, and even in a case where therecording linear velocity is different at least twice between theminimum linear velocity and the maximum linear velocity, it will bepossible to properly form amorphous record marks on the opticalrecording medium.

In the same manner, the relation between formation of an amorphous phaseand the recording linear velocity in the case of realizing an opticalrecording medium wherein the minimum linear velocity and the maximumlinear velocity in recording information on the optical recording mediumare different at least twice by a combination of any one of the aboverecording methods DVD1-1, 1-2 and 1-2 and any one of the above recordingmethods DVD2-1, 2-2 and 2-3 (for example, an optical recording medium tobe used at the minimum linear velocity being 2-times velocity, 2.5-timesvelocity or 3-times velocity of the reference linear velocity and at themaximum linear velocity being 6-times velocity of the reference linearvelocity, or an optical recording medium to be used at the minimumlinear velocity being 2-times velocity, 2.5-times velocity, 3-timesvelocity or 4-times velocity of the reference linear velocity and at themaximum linear velocity being 8-times velocity of the reference linearvelocity) will be described with reference to FIG. 4. For example, in acase where the minimum linear velocity is 2-times velocity of thereference linear velocity, and the maximum linear velocity is 8-timesvelocity of the reference linear velocity, by using the recording layercomposition and the layer structure of the optical recording medium ofthe present invention and/or the recording method of the presentinvention, it will be possible to make the cooling rate of the opticalrecording medium to be at least R_(c) at every linear velocity as shownby curve d in FIG. 4, and even in a case where the recording linearvelocity is different at least twice between the minimum linear velocityand the maximum linear velocity, it will be possible to properly formamorphous record marks on the optical recording medium.

Curve a in FIG. 4 shows an example of the recording linear velocitydependency of the cooling rate of the recording layer in a case wherethe fixed pulse strategy of FIG. 1 is applied to a disk of aconventional structure wherein the sheet resistivity of the reflectivelayer is larger than 0.6 Ω/□. By this optical recording medium and therecording method, the cooling rate is smaller than R_(c) at every linearvelocity, whereby it is impossible to form amorphous record marks in therecording layer.

Curve b in FIG. 4 shows an example of the recording linear velocitydependency of the cooling rate of the recording layer in a case where afixed pulse strategy of FIG. 1 is applied with an optical recordingmedium having the heat dissipation effect improved by changing thereflective layer to one having a composition having a high heatdissipating effect as mentioned hereinafter, in order to realize theoptical recording medium of the present invention. Curve b is locatedabove curve a, and it is evident that with the optical recording mediumhaving curve b, amorphous marks are more readily formed at everyrecording linear velocity, as compared with the optical recording mediumhaving the recording linear velocity dependency of the cooling rate ofthe recording layer shown by curve a.

Further, curve c in FIG. 4 shows the recording linear velocitydependency of the cooling rate of the recording layer in a case wherethe after-mentioned recording pulse strategies of 2T base (the recordingpulse division methods (I) to (III)) are applied to a disk having theabove conventional layer structure.

Further, curve d in FIG. 4 shows an example of the recording linearvelocity dependency of the cooling rate of the recording layer in a casewhere the after-mentioned recording pulse division methods (I) to (III)are applied to a disk employing the above GeSbTe eutectic alloy or GeSbeutectic alloy for the recording layer. Curve d is located above curvec, and it is apparent that with the optical recording medium havingcurve d, amorphous marks are likely to be readily formed at everyrecording linear velocity.

At a high linear velocity, the cooling rate is sufficiently higher thanthe critical cooling rate R_(c) for forming an amorphous phase in therecording layer, whereby the heat dissipating effect of the reflectivelayer is not distinctly influential over formation of the amorphousphase. However, at a low linear velocity, the cooling rate of therecording layer decreases as a whole, whereby the cooling rate becomeslower than the vicinity of R_(c), whereby the heat dissipating effect ofthe reflective layer over the formation of the amorphous phase will bedistinct.

On the other hand, these curves may be deemed to be the linear velocitydependency of the inverse number 1/τ of time τ during which therecording layer is maintained at a temperature of at least thecrystallization temperature, in a case where amorphous marks in therecording layer are recrystallized by a recording laser beam having anerasing power Pe (right hand side vertical axis in FIG. 4). If thisholding time τ is longer than the critical crystallization time τ_(c)determined by the recording layer material, i.e. 1/τ<1/τ_(c), amorphousmarks will be sufficiently recrystallized and erased. In the presentinvention, the above-mentioned recording layer material having aparticularly high crystallization speed is employed, whereby τ_(c) willbe small, and R_(c) will be large.

Further, with CD-RW, when a simple periodic signal comprising 3T markand 3T space is recorded and then a simple periodic signal comprising a11T mark and a 11T space is overwritten, if the erase ratio of the 3Tmark is adjusted to be at least 20 dB, usually, 1/τ<1/τ_(c), wherebyamorphous marks will be sufficiently recrystallized, and erasing ofrecord marks will be properly carried out.

Likewise, with RW-DVD, when a simple periodic signal comprising 3T markand 3T space is recorded and then, a simple periodic signal comprising a14T mark and a 14T space is overwritten, if the erase ratio of the 3Tmark is adjusted to be at least 20 dB, usually, 1/τ<1/τ_(c), wherebyamorphous marks will be sufficiently recrystallized, and erasing ofrecord marks will be properly carried out.

When the recording layer material of the above-mentioned GeSbTe eutecticalloy or GeSb eutectic alloy having a high crystallization speed, isemployed, τ_(c) can be reduced, and erasing at a high speed in a shorttime will be possible, while there will be a situation such that R_(c)is extremely high, and amorphous marks tend to be hardly formed.

Accordingly, with the optical recording material of the presentinvention, it is important to have such a characteristic as curve dwhereby 1/τ<1/τ_(c) is satisfied so that sufficient erasing can becarried out by overwriting at a high linear velocity, and at the sametime an opposing requirement such that the cooling rate at a low linearvelocity is made higher than R_(c), is satisfied. To obtain such amedium, it is necessary to select the compositions and thicknesses ofthe respective layers and to employ the after-described 2T base pulsestrategy.

From the above-mentioned viewpoint, as the material for the reflectivelayer, it is preferred to employ an alloy containing as the maincomponent Al or Ag having a high thermal conductivity and high heatdissipating effect. With the alloy containing Al or Ag as the maincomponent, the specific heat of the reflective layer is similar to thatof pure Al or pure Ag, and is considered to undergo no substantialchange by an addition of a trace amount of elements or by reducing thelayer thickness. Accordingly, the heat dissipating effect depends on thethermal conductivity and the thickness of the reflective layer.

Generally, the thermal conductivity of a thin film is substantiallydifferent from the thermal conductivity in a bulk state and is usuallysmaller, and by the influence of an island structure in the initialstage of deposition for forming the thin layer, the thermal conductivitymay sometimes decrease by at least one figure. Further, depending uponthe deposition condition, the crystallinity or the amount of impuritiestends to be different, and accordingly, even if the target to be usedfor deposition by sputtering is of the same composition, the thermalconductivity of the thin film may sometimes be substantially differentdepending upon the deposition condition.

Here, “proper” or “improper” of the thermal conductivity can be judgedby using the electrical resistance, since the thermal conductivity andthe electrical conductivity are in a good proportional relation with amaterial, like a metal film, wherein the heat conduction or the electricconduction is carried out mainly by movement of electrons. Theelectrical resistance of a thin film is represented by the electricalresistivity defined by the film thickness or the area of the measuredregion. Among the electrical resistivities, the volume resistivity andthe sheet resistivity (specific resistance) can be measured by a usualfour probe method and is stipulated in JIS K7194. By measuring thevolume resistivity and the sheet resistivity by means of this four probemethod, the thermal conductivity of the thin film can be judged far moresimply and with better reproducibility than actually measuring thethermal conductivity of the thin film itself.

The heat dissipating effect of the reflective layer is represented by aproduct of the thermal conductivity and the film thickness, andconsequently, the heat dissipating effect can be defined by the sheetresistivity.

In the present invention, the sheet resistivity is made to be usually atmost 0.55 Ω/□, preferably at most 0.4 Ω/□, more preferably at most 0.3Ω/□, particularly preferably at most 0.2 Ω/□, most preferably 0.18 Ω/□,in order to obtain a CD-RW medium overwritable at a wide range of linearvelocity from 8-times velocity to 24-times velocity, or from 10-timesvelocity to 32-times velocity, or to obtain a RW-DVD medium overwritableat a wide range of linear velocity of from 4-times velocity to 10-timesvelocity, or from 4-times velocity to 12-times velocity. On the otherhand, with a view to improving the heat dissipation of the reflectivelayer, the smaller the sheet resistivity, the better. However, the sheetresistivity is made to be usually at least 0.05 Ω/□, preferably at least0.1 Ω/□.

Further, a preferred reflective layer has a volume resistivity of atmost 150 nΩ·m, particularly at most 100 nΩ·m. On the other hand, amaterial having a volume resistivity being extremely small can hardly beobtainable in a thin film state, and it is usually at least 20 nΩ·m. Inorder to bring the above sheet resistivity within a range of from 0.05to 0.2 Ω/□, it is preferred that the volume resistivity is made to be aslow as from 20 to 40 nΩ·m.

The thickness of the reflective layer is usually at least 40 nm,preferably at least 50 nm and on the other hand, usually at most 300 nm,preferably at most 200 nm. If it is too thick, no adequate heatdissipating effect can be obtained, and the recording sensitivity tendsto deteriorate, although the sheet resistivity may be lowered. This isconsidered to be attributable to the fact that if the film thickness isthick, the thermal capacity per unit area increases, whereby it takestime for heat dissipation, and the heat dissipating effect rather tendsto be small. Further, with such a thick film, it takes time fordeposition, and also the material cost tends to increase. On the otherhand, if the film thickness is too thin, the influence of the islandstructure at the initial stage of the film growth tends to result,whereby the reflectivity or the thermal conductivity may sometimesdecrease.

As the material for the reflective layer, an Al alloy or an Ag alloy maybe mentioned. More specifically, the material for the reflective layersuitable for the present invention may be an Al alloy comprising Al andat least one element selected from the group consisting of Ta, Ti, Co,Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo and Mn. By using such an alloy, thehillock resistance can be improved. Accordingly, such an alloy can beemployed taking into consideration the durability, the volumeresistivity, the film-forming speed, etc. The content of theabove-mentioned element is usually at least 0.1 atomic %, preferably atleast 0.2 atomic % and on the other hand, usually at most 2 atomic %,preferably at most 1 atomic %. With respect to the Al alloy, if theamount of the additive impurity is too small, the hillock resistancetends to be inadequate in many cases, although such may depend also onthe deposition condition. Further, if the amount of the additiveimpurity is too large, it tends to be difficult to obtain a lowresistivity.

As the Al alloy, an Al alloy containing from 0 to 2 wt % of Si, from 0.5to 2 wt % of Mg and from 0 to 0.2 wt % of Ti, may also be used. Si iseffective to suppress fine peeling defects, but if the content is toolarge, the thermal conductivity may change with time. Accordingly, it ismade to be usually at most 2 wt %, preferably at most 1.5 wt %. Mgimproves the corrosion resistance of the reflective layer, but if thecontent is too large, the thermal conductivity may change with time.Accordingly, it is made to be usually at most 2 wt %, preferably at most1.5 wt %. Ti is effective to prevent fluctuation of the sputtering rate,but if the content is too large, the thermal conductivity tends todeteriorate, and casting of a bulk having Ti uniformly solid-solubilizedat a microlevel, tends to be difficult, and the target cost tends toincrease. Accordingly, it is adjusted to be usually at most 0.2 wt %.

Further, another preferred example of the reflective layer material maybe an Ag alloy comprising Ag and at least one element selected from thegroup consisting of Ti, V, Ta, Nb, W, Co, Cr, Si, Ge, Sn, Sc, Hf, Pd,Rh, Au, Pt, Mg, Zr, Mo and Mn. In a case where the archival stability ismore important, Ti, Mg or Pd is preferred as the additive component. Thecontent of the above element is usually at least 0.1 atomic %,preferably at least 0.2 atomic % and on the other hand, usually at most2 atomic %, preferably at most 1 atomic %.

In the present invention, by using a reflective layer material havingsuch a high thermal conductivity, it is possible to obtain a relativelythin reflective layer of at most 300 nm, having a properly small rangeof sheet resistivity at a level of from 0.2 to 0.55 Ω/□. Further, atleast, the additive element is adjusted to be at most 2 atomic %; thedeposition rate and the vacuum degree are adjusted to be as mentionedhereinafter; impurity atoms such as oxygen inevitably included duringthe deposition are controlled to be generally at most 1 atomic %; thevolume resistivity is adjusted to be from 20 to 40 nΩ·m; the filmthickness is adjusted to be at least 100 nm, preferably at least 150 nm,whereby a low sheet resistivity of from 0.05 to 0.2 Ω/□ can be obtained.

When another element is added to Al or Ag, it is common that the volumeresistivity increases in proportion to the added concentration. Additionof such another element is considered to lower the thermal conductivityby increasing electron scattering at the grain boundaries usually byreducing the crystal grain size. Accordingly, by adjusting the contentof such additive element, the crystal grain size can be made large,whereby the high thermal conductivity of the material itself can beobtained.

Further, the reflective layer is formed usually by sputtering or vacuumvapor deposition, and it is preferred to adjust the amount of impuritiesof the target or the vapor deposition material itself, or the amount oftotal impurities including the amount of moisture or oxygen includedduring the deposition, is controlled to be less than 2 atomic %. Forthis purpose, when the reflective layer is formed by sputtering, it ispreferred to control the ultimate degree of vacuum in the processchamber to be less than 1×10³ Pa.

Otherwise, if deposition is carried out at a background vacuum pressurepoorer than 10⁻⁴ Pa, it is preferred to adjust the deposition rate to beat least 1 nm/sec, preferably at least 10 nm/sec, to prevent inclusionof impurities. Or, in a case where the additive element is intentionallyincorporated more than 1 atomic %, it is preferred to adjust thedeposition rate to be at least 10 nm/sec to prevent inclusion ofadditional impurities as far as possible.

In order to attain a higher thermal conductivity and higher reliability,it is also effective to have the reflective layer multi-layered. In sucha case, it is preferred that at least one layer is made of theabove-mentioned material having a low volume resistivity having a filmthickness of at least 50% of the total thickness of the reflectivelayer. This layer substantially governs the heat dissipating effect, andother layers contribute to improvement of the corrosion resistance, theadhesion with the protective layer and the hillock resistance.Particularly when the first layer of the reflective layer containing Agas the main component, is formed in contact with the protective layercontaining e.g. ZnS containing sulfur, a second layer of the reflectivelayer containing no sulfur (in this specification, this layer may bereferred to as an interfacial layer) is formed in order to preventcorrosion by the reaction of Ag with sulfur. As the material to be usedfor the interfacial layer, a dielectric material or a metal material maybe mentioned. As a specific material, SiO₂, GeCrN, Ta, Nb or Al may, forexample, be mentioned. For the interfacial layer, a metal which mayfunction as a reflective layer may of course be employed. The thicknessof the interfacial layer is usually at least 1 nm, preferably at least 2nm and on the other hand, usually at most 10 nm, preferably at most 7nm. In the case of employing a metal material, it is particularlypreferred to adjust the thickness of the interfacial layer to be from 2nm to 7 nm.

In the present invention, it is further necessary to pay attention tothe construction of the groove provided on the substrate to secureretrieving interchangeability with CD or DVD.

3-1. In the Case of CD-RW

The track pitch of a groove is usually about 1.6 μm±0.1 μm. Further, thedepth of the groove is usually from 30 to 45 nm, particularly preferablyfrom about 30 to 40 nm.

If the groove depth is too deep, the push-pull value after recordingtends to be too large. Further, the radial contrast value afterrecording tends to be too large as compared with the value beforerecording, whereby there may be a problem in the stability of servo.

On the other hand, if the groove depth is too shallow, the radialcontrast value or the push-pull value is likely to be lower than thelower limit stipulated in CD-RW standards like Orange Book, Part 3.Further, the recording layer confinement effect by groove walls tends tobe weak, whereby deterioration due to repeated overwriting tends to beaccelerated. Further, if the groove depth is made too shallow, theproduction of a stamper for molding of the substrate tends to bedifficult.

Within the above range, the reflectivity in the groove will besufficiently high; 15% as the lower limit value in CD-RW standards caneasily be satisfied; and the push-pull amplitude Pa after recording willnot be too large, and even with a conventional concavo-convex pitretrieving circuit, it is possible to minimize the possibility that thegain of the push-pull detecting circuit is saturated.

The groove width is usually at least 0.5 μm, preferably at least 0.55 μmand usually at most 0.7 μm, preferably at most 0.65 μm. If the groovewidth is too small, the absolute value of the radial contrast afterrecording tends to hardly satisfy the stipulated value of less than 0.6.On the other hand, if the groove width is too large, deterioration ofthe overwriting durability caused by the presence of wobble tends to bedistinct. The groove width is preferably made wide as compared withconventional CD-RW to be overwritten at about 10-times velocity.

The mechanism of the deterioration of the durability accelerated by thepresence of wobble is not clearly understood, but it is considered to beattributable to the fact that a part of the recording laser beam hasbecome readily applied to the side walls of the groove. Namely, thefocused laser beam controlled by tracking servo will not follow thewobbling of the wobble and will advance straight along the center of thegroove for scanning, and therefore, if there is wobbling of the groovewalls, the laser beam is likely to be irradiated to such groove wallsthough slightly. At a groove wall portion or a groove corner portionwhere the adhesion of a thin film is poor, deterioration by heat damageduring repeated overwriting is likely to take place for such a reasonthat a stress concentration is likely to take place, and accordingly, itis considered that even a part of the laser beam is irradiated at such aportion, deterioration will be accelerated. In general, there is atendency that the durability will be improved by increasing the groovedepth and reducing the groove width in recording in the groove of aphase-change medium. However, in a case where wobble is present, if thegroove width is too small, the above-mentioned phenomenon ofdeterioration of the groove walls may rather be distinct.

Further, the groove width and the groove depth may be obtained by anoptical diffraction method by U-groove approximation by means of e.g. aHe—Ne laser beam having a wavelength of 633 nm. Further, thegroove-shape can actually be measured by a scanning electron microscopeor a scanning probe microscope. For the groove width in such a case, itis usually preferred to employ a value at a position halfway in thegroove depth.

With the optical recording medium of the present invention, recording bya CAV system, is possible. Namely, with the medium of the presentinvention, recording of data can be carried out while the rotationalspeed is maintained to be constant irrespective of the radial positionwhere the recording is carried out. In such a case, also retrieving canbe carried out at a constant rotational speed, and it is preferred tocarry out recording and retrieving at the same rotational speed.

3-2. In the Case of RW-DVD

The track pitch of a groove is usually about 0.74 μm±0.01 μm. Further,the depth of the groove is usually from 20 to 40 nm, particularlypreferably from about 25 to 35 nm.

If the groove depth is too deep, jitter of the recording signal willincrease.

On the other hand, if the groove depth is too shallow, the radialcontrast value or the push-pull value is likely to be lower than thelower limit stipulated in RW-DVD standards. Further, the recording layerconfinement effect by groove walls tends to be weak, wherebydeterioration due to repeated overwriting tends to be accelerated.Further, if the groove depth is made too shallow, the production of astamper for molding of the substrate tends to be difficult.

Within the above range, the reflectivity in the groove will besufficiently high; 18% as the lower limit value in RW-DVD standards caneasily be satisfied; and stabilized servo and sufficient push-pullsignals can be secured.

The groove width is usually at least 0.25 μm, preferably at least 0.28μm and usually at most 0.36 μm, preferably at most 0.34 μm. If thegroove width is too small, jitter of record signals tends todeteriorate, and it becomes difficult to adjust the reflectivity to beat least 18%. On the other hand, if the groove width is too large, thetrack cross signal value after recording is likely to be lower than thelower limit in phase-change type rewritable DVD standards, orinterference of wobbling between the adjacent tracks tends to be large,whereby jitter of record signals is likely to deteriorate.

The mechanism of the deterioration of the durability accelerated by thepresence of wobble is not clearly understood, but it is considered to beattributable to the fact that a part of the recording laser beam hasbecome readily irradiated to the side walls of the groove. Namely, thefocused laser beam controlled by tracking servo will not follow thewobbling of the wobble and will advance straight along the center of thegroove for scanning, and therefore, if there is wobbling of the groovewalls, the laser beam is likely to be applied to such groove wallsthough slightly. At a groove wall portion or a groove corner portionwhere the adhesion of a thin film is poor, deterioration by heat damageduring repeated overwriting is likely to take place for such a reasonthat a stress concentration is likely to take place, and accordingly, itis considered that even a part of the laser beam is irradiated at such aportion, deterioration will be accelerated. In general, there is atendency that the durability will be improved by increasing the groovedepth and reducing the groove width in recording in the groove of aphase-change medium. However, in a case where wobble is present, if thegroove width is too small, the above-mentioned phenomenon ofdeterioration of the groove walls may rather be distinct.

Further, the groove width and the groove depth may be obtained by anoptical diffraction method by U-groove approximation by means of e.g. aHe—Cd laser beam having a wavelength of 441.6 nm. Further, thegroove-shape can actually be measured by a scanning electron microscopeor a scanning probe microscope. For the groove width in such a case, itis usually preferred to employ a value at a position halfway in thegroove depth.

With the optical recording medium of the present invention, recording bya CAV system, is possible. Namely, with the medium of the presentinvention, recording of data can be carried out while the rotationalspeed is maintained to be constant irrespective of the radial positionwhere the recording is carried out. In such a case, also retrieving canbe carried out at a constant rotational speed, and it is preferred tocarry out recording and retrieving at the same rotational speed.

4. Regarding the Recording Method

In the present invention, by carrying out overwriting by the followingrecording method (recording pulse division method (I)) relating to thethird aspect of the present invention, rewriting of information canproperly be carried out at a recording linear velocity of from 10 to32-times velocity of CD-RW or of from about 6 to 12-times velocity ofRW-DVD. As a result, recording of signals excellent in theinterchangeability with the current CD retrieving system will bepossible.

The recording pulse division method (I) is one intended to obtain betterrecording signals by expanding variable parameters and their ranges thanthe recording methods CD1-1, 1-2, 1-3, 2-1 and 2-2 and recording methodDVD1-1 as described with reference to FIGS. 3 and 16.

That is,

Recording Pulse Division Method (I):

A recording method to be used for a rewritable optical recording medium,which comprises recording information by a plurality of record marklengths and space lengths between record marks, wherein:

between record marks, a laser beam having an erasing power Pe capable ofcrystallizing an amorphous phase is applied to form spaces betweenrecord marks, and

when the time length of one record mark is represented by nT (where T isthe reference clock period), for a record mark of n=2m (where m is aninteger of at least 1), of which the time length (n−j)T (where j is areal number of from −2.0 to 2.0) is divided into m sections of α_(i)Tand β_(i)T comprising α₁T, β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T(provided that Σ_(i)(α_(i)+β_(i))=n−j), and for a record mark of n=2m+1(where m is an integer of at least 1), of which the time length (n−k)T(where k is a real number of from −2.0 to 2.0) is divided into msections of α_(i)′T and β_(i)′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . ., α_(m)′T and β_(m)′T (provided that Σ_(i)(α_(i)′+β_(i)′)=n−k), a laserbeam having a constant writing power Pw sufficient to melt the recordinglayer is applied within a time of α_(i)T and α_(i)′T (where i is aninteger of from 1 to m), and a laser beam having a bias power Pb isapplied within a time of β_(i)T and β_(i)′T (where i is an integer offrom 1 to m); and further,

when m≧3,

for a record mark of n=2m, when the start time for nT mark isrepresented by T₀,

(i) after a delay time T_(d1)T from T₀, α₁T is generated, then,

(ii) within i=2 to m, β_(i−1)T and α_(i)T are alternately generated inthis order, while β_(i−1)+α_(i) maintains about period 2 (provided thatat i=2 and/or i=m, β_(i−1)+α₁ may be deviated from about period 2 withina range of ±0.5, and when m≧=4, β_(i−1) and α_(i) take constant valuesβc and αc, respectively, within i=3 to m−1), and then,

(iii) β_(m)T is generated, and

for a record mark of n=2m+1, when the start time for nT mark isrepresented by T₀,

(i) after a delay time T_(d1)′T from T₀, α₁′T is generated, then,

(ii) within i=2 to m, β_(i−1)′T and α_(i)′T are alternately generated inthis order, while β_(i−1)′+α_(i)′ maintains about period 2 (providedthat at i=2 and/or i=m, β_(i−1)′+α_(i)′ may be deviated from aboutperiod 2 within a range of ±2, and when m≧4, β_(i−1)′ and α_(i)′ takeconstant values βc and αc, respectively, within i=3 to m−1), and then,

(iii) β_(m)′T is generated, and

with the same m, for a record mark of n=2m and a record mark of n=2m+1,α_(m)≠α_(m)′, and at least one set selected from (T_(d1), T_(d1)′), (α₁,α₁′), (β₁, β₁′), (β_(m−1) and β_(m−1)′) and (β_(m) and β_(m)′) takesdifferent values.

In the foregoing, when m=at least 3, T_(d1), α₁, β₁, α_(c), β_(c),β_(m−1), α_(m) and β_(m) are preferably constant irrespective of m.

Likewise, when m=at least 3, T_(d1)′, α₁′, β₁′, β_(m−1)′, α_(m)′ andβ_(m)′ are also preferably constant irrespective of m.

Further, in the EFM modulation system to be used for CD-RW, thisrecording system is applied using sets of (6,7), (8,9) and (10,11) for nin the case where m is at least 3. On the other hand, in the case ofEFM+ modulation to be used for RW-DVD, it is necessary to consider n=14in addition to the above sets of n, but in the recording pulse divisionmethod of n=10, two pairs of α_(c)T and β_(c)T may simply be addedbetween α₁T and α_(m)T.

Here, when n=2, after a delay time T_(d1)T, a writing power Pw isapplied at section α₁T, and then a bias power Pb is applied at sectionβ₁T, to form an amorphous mark.

Further, when n=3, after a delay time T_(d1)′T, a writing power Pw isapplied at section α₁′T, and then a bias power Pb is applied at sectionβ₁′T, to form an amorphous mark.

Further, in a case where the above recording method is applied as arecording method up to 32-times velocity of CD-RW, it is preferred toadopt the following recording conditions. Namely, the recording linearvelocity is set to be a linear velocity of at most 32 times thereference linear velocity V₁=1.2 to 1.4 m/s, and EFM modulationinformation is recorded by a plurality of record mark lengths and spacelengths between record marks, wherein the time length of one record markis set to be nT (where n is an integer of from 3 to 11), the ratio of anerasing power Pe to a writing power Pw is set to be Pe/Pw=0.2 to 0.6,and a bias power Pb is set to be Pb≦=0.2Pe.

Further, in a case where the above recording method is applied as arecording method up to 12-times velocity of RW-DVD, it is furtherpreferred to adopt the following recording condition. Namely, therecording linear velocity is set to be a linear velocity of at most 12times the reference linear velocity V₁=3.49 m/s, and EFM+ modulationinformation is recorded by a plurality of record mark lengths and spacelengths between record marks, wherein the time length of one record markis set to be nT (where n is an integer of from 3 to 11 and 14), theratio of an erasing power Pe to a writing power Pw is set to bePe/Pw=0.2 to 0.6, and a bias power Pb is set to be Pb≦0.2Pe.

In the present invention, the method for controlling the energy of therecording laser energy beam is generally called a recording pulsestrategy or a pulse strategy. Particularly, the method in which a nTmark is formed by a pulse train of a plurality of divided writing powerlevels, is called divided recording pulses, a recording pulse divisionmethod or a pulse division method.

This recording pulse division method is preferably employed usually at avelocity of from 8-times velocity to 24-times velocity or 32-timesvelocity as a recording method for overwritable CD-RW.

Or, it is preferably employed usually at a velocity of from 2-timesvelocity to 12-times velocity as a recording method for overwritableRW-DVD.

FIG. 5 is a timing chart for illustrating an example of the relation ofthe respective recording pulses in a case where the pulse divisionmethod is carried out in the recording method of the present invention.Electronic circuits (integrated circuits) for controlling theirradiation timings of the respective laser beams for writing power Pw,bias power Pb and erasing power Pe, in the recording device to carry outrecording of information on an optical recording medium, are designed,based on the timing chart shown in FIG. 5. FIG. 5 shows a case whereinPb≦Pe≦Pw, the writing power at the recording pulse section α_(i)T (i=aninteger of 1 to m) is constant at Pw, the bias power at off-pulsesection β_(i)T (i=integer of 1 to m) is constant at Pb, and the powerfor irradiation at spaces between marks and at sections other thanα_(i)T (i=1 to m) and β_(i)T (i=1 to m) is the erasing power Pe which isconstant. Pe/Pw is adjusted to be usually at least 0.2, preferably atleast 0.25. On the other hand, Pe/Pw is adjusted to be usually at most0.6, preferably at most 0.4. Within the above range, Pe/Pw is preferablya value of from 0.2 to 0.6, particularly preferably a value within arange of from 0.2 to 0.4, more preferably within a range of from 0.25 to0.4. If this ratio is smaller than the above range, the erasing power istoo low, whereby unerased amorphous marks are likely to remain, and ifit is larger than the above range, the portion irradiated with Pe islikely to be amorphous again after being melted.

In FIG. 5, 500 represents a reference clock having period T.

FIG. 5(a) shows a pulse waveform corresponding to a record mark havinglength nT, and symbol 501 corresponds the length of the record markhaving length nT. In FIG. 5(a), a case where n=11 and m=5, is shown.FIG. 5 shows an example of an odd number mark, but to simply thedescription, in the description of FIG. 5 and the following, when an oddnumber mark and an even number mark are described, unless otherwisespecified, the respective parameters of α_(i), β_(i), T_(d1), T_(d2),T_(d3) and j will be used as representatives. Namely, in the descriptionwhere n is an even number mark, the above parameters may be used as theyare, and in the description where n is an odd number mark, the aboveparameters may be substituted by α_(i)′, β_(i)′, T_(d1)′, T_(d2)′,T_(d3)′ and k, respectively.

Against the recording method for conventional CD-RW or RW-DVD shown inFIG. 1, the significance of the present recording method shown in FIG.5, is as follows.

If j is 0, Σ_(i)(α_(i)+β_(i))/m=n/m. Thus, n/m is a value correspondingto an average length of (α_(i)+β_(i)), and (n/m)T will be a valuecorresponding to an average period of divided pulses.

In the optical recording method of the present invention, in a casewhere n=2m or n=2m+1, the division number of recording pulses will be m,and n/m will be about 2. Namely, by adjusting the average period forrepetition comprising a recording pulse and an off-pulse to be generally2T, the lengths of α_(i)T and β_(i)T can be made sufficient. Forexample, recording pulse section α_(i)T and off-pulse section β_(i)T canbe taken to be sufficiently longer than 0.5T and even if the datareference clock period T at 32-times velocity of CD became about 7.2nsec or even if the data reference clock period at 12-times velocity ofDVD becomes about 3.5 nsec, heating of the recording layer can besufficiently carried out, while supply of heat by the subsequent pulsescan be suppressed, so that sufficient cooling effects can be obtained.

In the division method disclosed in conventional CD-RW or RW-DVDstandards, m is fixed to m=n−1, and thus, n/m=n/(n−1). This valuebecomes small as n increases, and accordingly, when the longest marktime length is represented by n_(max)T, n/m will be minimum at n_(max).Namely, the average period of repetition comprising a recording pulseand an off-pulse (in this specification, this average period ofrepetition comprising a recording pulse and an off-pulse may sometimesbe referred to as an average period of divided pulses) is longest withthe shortest mark and shortest with the longest mark, and accordingly,α_(i)T or β_(i)T is shortest at the longest mark.

For example, in the EFM modulation system, n=3 to 11 and k=1, andtherefore, (n_(max)/m)=11/(11−1)=1.1

Further, for example, in the EFM+ modulation system, n=3 to 11 and 14,and k=1, and therefore, (n_(max)/m)=14/(14−1)=1.08.

Namely, the average of repeating periods (divided pulses) in the EFMmodulation system and the EFM+ modulation system, is generally 1T.

In this specification, the conventional pulse division method defined inFIG. 1 is referred to as “1T base” pulse strategy, and the pulsedivision method of the present invention as defined in FIG. 5 isreferred to as “2T base” pulse strategy.

At least 24-times velocity of CD or at least 4-times velocity of DVD,when the data reference clock period T becomes less than about 10 nsec,in the longest mark, the average period of divided pulses generallybecomes less than 10 nsec. This means that the average of divided pulsesin the 1T base pulse strategy becomes shorter than 10 nsec. And, in sucha case, the average value of recording pulse section α_(i)T or theaverage value of off-pulse section β_(i)T becomes less than 5 nsec.Further, in the above description, even if a certain α_(i) or β_(i) ismade to be longer than the average value, such means that another β_(i)or α_(i) becomes shorter, and thus, there is no difference in thateither one α_(i)T or β_(i)T becomes small. And, if either one of α_(i)Tor β_(i)T becomes less than 5 nsec, especially less than 3 nsec, theremay be a case where in high velocity recording, beam irradiation andcooling time can not sufficiently be secured.

Record marks in the present invention are, usually, recognized asphysical marks which are continuously formed in the recording medium andwhich can be optically distinguishable from other portions. Namely, arecord mark may be formed from a plurality of physical marks. When thenumerical aperture of the object lens for focusing the retrieving laseris represented by NA, and the retrieving laser wavelength is representedby λ, if physical marks are closer than 0.2(λ/NA), such physical markscan hardly be optically distinguished. Accordingly, when one record markhaving mark length nT is to be formed of a plurality of physical marks,their distances are preferably adjusted to be smaller than 0.2(λ/NA).

Further, when the present invention is applied to CD-RW, it is preferredto adjust the average value of recording pulse sections α_(i)T (i=1 tom) and the average value of off-pulse sections β_(i)T (i=1 to m−1) to beat least 3 nsec to secure the time follow up nature of irradiated laserpower. More preferably, individual α_(i)T (i=1 to m) and β_(i)T (i=1 tom−1) are adjusted to be at least 3 nsec.

On the other hand, when the present invention is applied to RW-DVD, itis preferred to adjust both the average value of recording pulsesections α_(i)T (i=1 to m) and the average value of off-pulse sectionsβ_(i)T (i=1 to m−1) to be at least 2 nsec, to secure the time follow upnature of irradiated laser power.

Here, with respect to the time width of pulse α_(i)T (i=1 to m), in atransition of a logical level corresponding to the transition of thepower level between Pw and Pb in the divided pulse generating logicalcircuit as shown by the timing chart in FIG. 5, a logical level isdefined by the time until the output has reached from one level to ahalf level of the other level. Accordingly, for example, the time widthof the recording pulse of α_(i)T in FIG. 5 means an interval from thetime when a half level of the logical level is reached at the time ofthe change of the rising portion of the above pulse from Pb to Pw, tothe time when a half level of the logical level is reached at the timeof the change of the falling portion of the above pulse from Pw to Pb.Here, the logical levels are for example binary levels of 0 V and 5 V inTTL.

The reason as to why in CD, α_(i)T(β_(i)T) is preferably adjusted to beat least 3 nsec, while in DVD, α_(i)T(β_(i)T) is preferably adjusted tobe at least 2 nsec, will be explained. Namely, in the case of the DVDsystem, the diameter of the focused laser beam for recording is about70% of that in the case of the CD system. Accordingly, the spacialinfluence which one recording pulse irradiation will give, will be alsoabout 70%. Thus, the diameter of the focused laser beam becomes small,and the spacial resolution will be improved, whereby a short time pulseirradiation at a level of 2 nsec which is about 70% of 3 nsec, becomeseffective. Further, with a small beam system, the area to be heated issmall, whereby cooling is fast, and also with respect to an off-pulsesection, even if it is shortened to a level of 2 nsec, sufficientcooling effects can be obtained. However, also in the case of RW-DVD, atleast 3 nsec is more preferred.

In the present invention, β_(m) may be 0, so that no beam is applied toβ_(m)T i.e. the last off-pulse section. However, in a case where theheat accumulation problem at the rear end portion of a mark issubstantial, it is preferred to provide β_(m)T. In such a case, β_(m)Tis also adjusted to be at least 2 nsec, more preferably at least 3 nsec.Here, the pulse time width of β_(m)T is defined by the time when a halfof the logical level has been reached in the transition of the logicallevel between Pb and Pe, like in the case of the above-mentioned α_(i)T.

Actual divided pulses for irradiation of a laser beam are formed byusing a timing chart as shown as an example in FIG. 5 and by inputtingan integrated circuit output of a logical level for generating a gatesignal to a laser drive circuit, to control a large current for laserdriving thereby to control a laser output from a laser diode to controlthe writing power. In the present invention, as mentioned above, thepulse width is defined based on the time width at the logical level. Theactual output laser waveform will have a delay of from about 1 to 3 nsecand at the same time will be accompanied by overshooting orundershooting. Accordingly, the change with time of the writing power isnot of a simple square waveform as shown in FIG. 3. However, in therecording pulse division method in the present invention, when recordingpulse sections α_(i)T (i=1 to m) are at least 2 nsec, an irradiationenergy required for recording can be secured by increasing writing powerPw_(i), although there may be a problem of the rising/falling of therecording beam. Also in such a case, by adjusting the rising and fallingof the actual recording laser beam pulses to be less than 2 nsec, morepreferably less than 1.5 nsec, more preferably less than 1 nsec, thenecessary writing power Pw can be controlled. Further, the actualwriting power rising time or falling time is usually meant for the timerequired for transition from 10% to 90% as the difference from one levelto another level when the power transfers between the power levels of Peand Pw or when the power transfers between the power levels of Pb andPw. The sum of the rising and falling is smaller than the time width ofα_(i)T, preferably at most 80% of α_(i)T, more preferably at most 50% ofα_(i)T.

In the recording pulse division method of the present invention, even ifthere is a discrepancy between the time width of the logical level andthe actual response of the writing power, there is no problem so long asit is a delay at a level of the above rising or falling time. With adelay of such a level, proper recording can be carried out within thepreferred variable ranges of the respective parameters defining therecording pulse division method, as described later (defined bytheoretical levels). Inversely, even with a laser diode outputnecessarily accompanied by such a delay or overshooting, etc., marklength modulation recording by the divided recording pulses will bepossible in a clock period of less than 10 nsec, which is an importantfeature of the recording pulse division method of the present invention.

On the other hand, when off-pulse sections β_(i)T (i=1 to m−1) are alsoat least 2 nsec, the cooling effects can be secured by lowering the biaspower Pb to the same level as the retrieving power Pr or to 0 so long asthere will be no adverse effect to other systems such as a trackingservo.

In order to obtain larger cooling effects, it is preferred thatΣ_(i)(α_(i)) is made to be smaller than 0.5 n with respect to timelengths of all record marks. More preferably, Σ_(i)(α_(i)) is at most0.4 n. Namely, the sum of recording pulse sections Σ_(i)(α_(i)T) is madeshorter than Σ_(i)(β_(i)T), so that off-pulse sections in each mark aremade to be longer. Particularly preferably, with respect to every i ofi=2 to m−1, α_(i)T≦β_(i)T, and at least in the recording pulse train ofthe second et seq, β_(i)T is made longer than α_(i)T.

In the recording method of the present invention, the values for α_(i)(i=1 to m) and β_(i) (i=1 to m−1) are optionally set depending upon thevalues for e.g. recording pulse sections α_(i)T (i=1 to m), off-pulsesections β_(i)T (i=1 to m−1), etc., but they are respectively usually atleast 0.01, preferably at least 0.05 and, except for a case where n=3,usually at most 2, more preferably at most 1.5. Especially with respectto β_(i) (i=1 to m−1), if the value is too small, the cooling effect maysometimes be inadequate, and it is preferably at least 0.1, particularlypreferably at least 0.3. On the other hand, if it is too large, a recordmark may sometimes be optically separated by too much cooling, and it isat most 2. However, with respect to β_(m)′ of the last off-pulse sectionin a case where n=3, it is at most 3, preferably at most 2.5, morepreferably at most 2. Further, in a modulation system containing n=2,the case of n=3 will likewise apply.

The effect of enlarging an off-pulse section is large at the firstoff-pulse section β₁T which presents a substantial influence over theshape of the forward end of a mark and at the last off-pulse sectionβ_(m)T which presents a substantial influence over the shape of the rearend of the mark. Among them, the influence over the last off-pulsesection β_(m)T will be particularly large.

In the present invention, Pb_(i)<Pw_(i), and Pb_(i)<Pw_(m+1), wherePw_(i) is the recording laser power applied to recording pulse sectionsα_(i)T (i=1 to m), and Pb_(i) is the recording laser power applied tooff-pulse sections β_(i)T (i=1 to m−1), and it is preferred that Pw andPb take constant values, respectively, in one recording pulse sectionand off-pulse section, irrespective of i and n. In order to obtain alarge cooling effect, it is preferred to set Pb<Pw with respect to timelengths of all record marks. More preferably, Pb/Pw≦0.2, furtherpreferably Pb/Pw≦0.1. Further, the bias power Pb may be made to be equalto a laser power Pr applied at the time of retrieving. As a result,setting of the divided pulse circuit required for pulse division will besimplified.

It is preferred that parameters α_(i) (i=1 to m) and β_(i) (i=1 to m−1)relating to the pulse width can be specified for a high resolution of atleast 1/16T. More preferably, they can be specified for an opticalresolution of at least 1/20T, more preferably at least 1/32T. With a lowresolution of less than ⅛, there may be a case where parameter valuesrelating to the optimum pulse width for proper recording can not befound out.

In such a case, it is possible to employ two or more different valuesfor Pb_(i) and/or Pw_(i) depending upon i, against the time length of aspecific one record mark.

For example, writing powers Pw_(i) and Pw_(m) at the forefront recordingpulse section α₁T and the last recording pulse section α_(m)T are madeto have values different from the writing power Pw at intermediaterecording pulse sections α_(i)T (i=2 to m−1), whereby the mark shapes atthe fore-end and rear-end portions of the mark may accurately becontrolled. In such a case, the writing power Pw at intermediaterecording pulse sections α_(i)T (i=2 to m−1) is preferably made to havethe same power value at every section, whereby setting of the dividedpulse circuit will be simplified. Likewise, with respect to the biaspower Pb_(i) at off-pulse sections β_(i)T (i=1 to m−1), it is preferablyset to have the same power value, except that only the bias power Pb_(m)at β_(m)T is set to have a value different from other Pbcomplementarily. Further, in order to properly record 3T marks, among atleast two record marks having different n, different Pw and/or Pb valuesmay be adopted for the same i. Namely, at the time of recording marklengths of n=4 or more, Pw and Pb are set to be constant, while only atthe time of recording a mark length of n=3, the writing power may be setto have a slightly different value (a difference of about 10%). Also insuch a case, Pb is preferably set to be constant.

In the present invention, primarily, only by is controlling a time(relating to a pulse width) parameter of any one of T_(d1), α₁, β₁,β_(m−1), α_(m) and β_(m), accurate mark length control and low jittercan be realized, and it is preferred for simplification of the circuit,fine adjustment of Pw₁, Pw_(m) or Pb_(m) is individually carried outonly in a case where there is some restriction in setting such timeparameters. Such a restriction may specifically be a case wherein theresolution to set parameter values relating to the pulse width is sorough that proper recording can not be done only by setting the pulsewidths.

The bias power Pb is preferably of substantially the same value as theretrieving power Pr of a retrieving laser beam required for retrieving.For CD-RW, it is usually of a value of at most 2 mW, preferably at most1.5 mW, more preferably at most 1 mW. On the other hand, for RW-DVD, itis usually of a value of at most 1 mW, preferably at most 0.7 mW, morepreferably at most 0.5 mW. So long as there will be no adverse effect tofocusing or tracking servo, it is preferably set to be as close aspossible to 0, whereby the quenching effect of the recording layer atthe Pb irradiation sections (off-pulse sections) will be accelerated.Further, the values for Pw, Pe and Pb may not necessarily be constant ina direct current fashion, and may, for example, have a high frequencysuperimposed in a cycle of at most about 1/10 of the clock period T,whereby the laser operation can be stabilized. In such a case, Pw, Peand Pb will be the respective average values.

FIG. 5(b) shows a recording pulse strategy (dotted line 502) in a casewhere n=11 i.e. m=5, which is formed by a combination of a plurality ofrecording pulse-controlling gates shown at 503, 504, 505 and 506.Namely, gate signal G1 (503) to form the first recording pulse α₁T, gatesignal G2 (504) to form middle recording pulses α_(i)T (2≦i≦m−1), gateG3 to form the last recording pulse α_(m)T (505) and gate G4 to definesections for application of Pe and Pb, are separately formed, and theyare combined. At G1, G2 and G3, writing powers will be emitted at levelON. Further, with gate signal G4, its ON-section has the rising of α₁Tas the base point (i.e. after a delay of T_(d1) from T₀), and theON-section of (n−j)T is set.

The preferential relation of such gate signals can be accomplished bycarrying out summing operation of logical signals for controlling therespective gates by letting ON-OFF of the gates correspond to logical 1or 0. Specifically, ON-signals of G1, G2 and G3 are preferred to anON-signal of reversed polarity signal of G4, so that even during the G4ON-period (even during irradiation with Pb), if G1, G2 or G3 becomes ON,Pw will be applied. As a result, gate signal G4 will define the timingof an off-pulse section β₁T at a section where each of G1, G2 and G3 isOFF.

The position of the forward end of a mark is substantially determined bythe rising of the writing power laser beam at α₁T, and the jitter isdetermined by powers Pw₁ and Pb₁ at α₁T and β₁T and the duty ratio ofα₁T to β₁T. With respect to β₁, so long as it is within a range of from0.5 to 2, a change at a level of 0.5 gives no substantial influence overthe forward end position of the mark or the jitter, and accordingly, itcan be used for controlling the difference 1T in the mark length betweenan even number length and an odd number length, which will be describedlater.

On the other hand, the rear end position of the mark depends on thefalling position of the last recording pulse α_(m)T or the subsequentcooling process of the recording layer temperature. Further, it dependson the power at the divided pulse (β_(m−1)+α_(m))T at the rear end ofthe mark, Pw_(m), Pb_(m) and the duty ratio of α_(m) to β_(m).Particularly, with a phase-change medium forming amorphous marks, italso depends on the value of the rear end off-pulse section β_(m)T whichgives a substantial influence over the cooling rate of the recordinglayer. With respect to β_(m−1), if it is within a range of from 0.5 to2, a change at a level of 0.5 gives no direct influence over the rearend position of the mark or the jitter, and accordingly, it can be usedfor controlling the difference 1T in the mark length between an evennumber length and an odd number length, which will be described later.However, as described hereinafter, in a case where an optical recordingmedium of the present invention capable of high velocity recording is tobe used for low velocity recording, it will be important to adjust alsoβ_(m)T.

In a case where the division number m is 3 or more, among intermediaterecording pulses present between the forefront pulse and the rear endpulse, β_(i−1)T and α_(i)T where i=2 to m, will be repeated with aperiod of generally 2T. Namely, β_(i−1)+α_(i) will be generally 2 (i=2to m). By making the period constant in such a manner, thepulse-generating circuit can be simplified. In the present invention,“generally” 2 or “generally” 2T is meant to express that a deviationfrom 2T which inevitably results from the practical nature of theelectronic circuit, etc., is allowable. Namely, a deviation more or lessfrom 2T is allowable so long as the effect of the present invention isobtainable such that proper recording is possible within a wide range ofrecording linear velocity of from 8 to 24-times velocity or from 8 to32-times velocity in the case of CD (from 2 to 10-times velocity or from2 to 12-times velocity in the case of DVD). For example, a deviation ata level of ±0.2 (from 1.8T to 2.2T) is included in the deviation from 2Twhich inevitably results from the practical performance of theelectronic circuit, etc.

In the case of an even number mark length, even at β₁+α₂ andβ_(m−1)+β_(m), their values can be made generally 2, and such ispreferred, since the pulse-generating circuit can be simplified.However, with respect to i=1 and/or i=m in an even number mark length,i.e. β₁+α₂ and/or β_(m−1)+α_(m), there may be a case where it is betterto allow a deviation from 2 within a range of ±0.5, so that an accuratemark length and control of jitter at the mark end can be possible. Insuch a case, β_(i−1)+α_(i) present between β₁+α₂ and β_(m−1)+α_(m) maybe made to be generally 2.

Further, also with respect to i=1 and/or i=m in an odd number marklength i.e. β₁′+α₂′ and/or β_(m−1)′+α_(m)′, it may be better to allow adeviation from 2, so that a more accurate mark length and control ofjitter at a mark end, will be possible. Namely, since β₁′=β₁+Δ₁,β_(m−1)′=β_(m−1)+Δ_(m−1) and α_(m)′=α_(m)+Δ_(m), β₁′+α₂′ and/orβ_(m−1)′+α_(m)′ should better allow a deviation from 2 for at least Δ₁,Δ_(m−1) and Δ_(m), whereby a more accurate mark length and control ofjitter at a mark end, will be possible. Accordingly, in such a case,β_(i−1)′+α_(i)′ present between β₁′+α₂+ and β_(m−1)′+α_(m)′, may be madeto be generally 2.

In this pulse generating method, the duty ratio of α_(i)T and β_(i−1)Tin middle recording pulses where i=2 to m−1, gives no influence over thejitter at the forward or rear end of the mark, and accordingly, it maybe any so long as amorphous marks can be formed with a prescribed width,and the signal amplitude can be secured. Accordingly, in order tosimplify the pulse-generating circuit, such a ratio is made to have aconstant value. Particularly in a case where m is 4 or more, whereintermediate pulses may be repeatedly present, α_(i)=αc (constant value)for every i which is at least 3 and at most (m−1) in record marks of twotypes i.e. an even number length mark and an odd number length mark inthe case of the same division number m. At the same time, period 2T isgenerally constant, and accordingly, β_(i)=2−αc will generally have aconstant value βc. In this sense, βc depends on αc and will bedetermined once αc is determined.

After all, when m is 3 or more (n=6 or more), fine adjustment is carriedout for period (β₁+α₂)T and/or (β_(m−1)+α_(m))T, whereby desired marklength nT will be accomplished. Here, it is preferred that also α₂ willalso take the same value αc as other α_(i) (i=3 to m−1) Further, in aneven number mark, it is preferred that also α_(m) takes the same valueαc. In this manner, designing of the control circuit for controlling thegeneration of laser beams (pulsed beams) for recording pulses andoff-pulses of the recording pulse strategy, can be simplified.

However, in a case where n=3, α₁ and β₁ will serve also as α_(m) andβ_(m), whereby it will be necessary to adjust the 3T mark length and thejitters at the forward and rear ends of the mark only by α₁ and β₁ asvalues different from other n.

Now, the recording pulse division method of 2T base of the presentinvention has a feature that based on a more highly regulated rule,consideration is given as to whether the value which n of nT mark cantake, is an odd number or an even number.

In the following description, explanations will be made again bydistinguishing parameters α_(i), β_(i), T_(d1), T_(d2), T_(d3) and Jcorresponding to the case of an even number mark length and parametersα₁′, β_(i)′, T_(d1)′, T_(d2)′, T_(d3)′ and k corresponding to the caseof n being an odd number mark length, with the same m.

In FIG. 5, times having T_(d1), T_(d2) and T_(d3) multiplied by T, aredefined as delay times from the forward end time T₀ of nT mark, butT_(d1), T_(d2) and T_(d3) are primarily intended to define the timingfor generation of recording pulse α₁T, forefront pulse α₂T among middlepulses and α_(m)T, respectively. It is optional where to take the basicpoint to accomplish such a purpose. For example, T_(d2) may be definedfrom the final point of α₁T, i.e. T_(d2)=β₁, or it may be defined fromthe starting point of α₁T so that T_(d2)=(α₁+β₁). Likewise, T_(d3) maybe defined by using T₀ as the basic point, but it may be defined byusing the falling of α_(m−1)T as the basic point, i.e. T_(d3)=β_(m−1).Inversely, by the definition of such delay times T_(d1), T_(d2), T_(d3),etc., β₁, β_(m−1) and β_(m) will be fixed. Namely, (m, T_(d1)′, α₁, β₁,αc, β_(m−1), α_(m), β_(m)) will be fixed as a set of independentparameters to univocally define the recording strategy of the presentinvention. Further, in a case where n is an odd number, as a set ofindependent parameters, (m, T_(d1)′, α₁′, β₁′, αc′, β_(m−1)′, α_(m)′,β_(m)′) will be fixed.

As mentioned above, essentially, it is sufficient that these parameters(timings for rising and falling of the respective recording pulses andoff-pulses) are fixed, and it is optional how to indirectly take thebasic points of parameters for delay times such as T_(d1), T_(d2) andT_(d3).

And, in order to record the mark length and space length nT for each nand to reduce the mark and space jitters as fluctuation thereof, foreach n, the division number m and at least two sets among (T_(d1)andT_(d1)′), (T_(d2) and T_(d2)′), (T_(d3) and T_(d3)′) (α₁ and α₁′),(α_(m) and α_(m)′) and (β_(m) and β_(m)′) are changed to generatedivided recording pulses. This also means that for every n, the divisionnumber m and at least two sets among (T_(d1) and T_(d1)′), (α₁ and α₁′),(β₁ and β₁′), (β_(m−1) and β_(m−1)′) (α_(m) and α_(m)′) and (β_(m) andβ_(m)′) are changed.

In the above recording method to change various parameters for each n,preferred is such that with the same m, for a record mark of n=2m and arecord mark of n=2m+1, α_(m)≠α_(m)′, and at least one set selected from(T_(d1), T_(d1)′), (α₁, α₁′), (β₁, β₁′), (β_(m−1) and β_(m−1)′) and(β_(m) and β_(m)′) takes different values.

Namely, especially when m is 3 or more, in order to impart mark lengthdifference T between an even number length mark and an odd number lengthmark with the same division number m, in the present invention,especially time lengths of the respective sections of β₁T, β_(m−1)T,α_(m)T and β_(m)T are adjusted. If only one parameter among these β₁,β_(m−1), α_(m) and Δ_(m) is changed to impart difference 1T between aneven number length mark and an odd number length mark, there may be anadverse effect to the formation of the front and rear ends of the oddnumber length mark. Therefore, when an odd number length mark is to beformed, a value other than 0 is added to α_(m) (to make α_(m)≠α_(m)′),while adding a value other than 0 to at least one of β₁, β_(m−1), andβ_(m) used for the formation of an even number length mark (to satisfyat least one of β₁≠β₁′, β_(m−1)≠β_(m−1)′ and β_(m)≠β_(m)′). This meansthat from the above definitions of T_(d1), T_(d2) and T_(d3), for aneven number length mark and an odd number length mark with the samedivision number m, α_(m)≠α_(m)′, and further, at least one set ofparameters among three sets of (T_(d2) and T₂′), (T_(d3) and T_(d3)′)and (β_(m) and β_(m)′) take different values depending on whether n isan even number or an odd number. Or, this means that for an even numberlength mark and an odd number length mark with the same division numberm, α_(m)≠α_(m)′, and further at least one set of parameters among threesets of (β₁ and β₁′), (β_(m−1) and β_(m−1)′) and (β_(m) and β_(m)′) takedifferent values depending upon whether n is an even number or an oddnumber.

In JP-A-2002-331936 or in literatures “Proceedings of PCOS2002, No.30-Dec. 1, 2002, pp. 52-55”, “Proc. SPIE Vol. 4090 (2000) pp. 135-143”,and “Proc. SPIE Vol. 4342 (2002), pp. 76-87”, some of the presentinventors have proposed that in order to properly realize a mark lengthdifference of 1T between an even number length mark and an odd numberlength mark with the same division m, mainly the lengths of β₁T andβ_(m−1)T are respectively corrected to β₁′T and β_(m−1)′T.

However, as a result of a study made by the present inventors, it hasbeen found that if with CD-RW, the recording linear velocity isincreased to 24-times velocity or 32-times velocity, or with RW-DVD, therecording linear velocity is increased to 8-times velocity or 10-timesvelocity, it tends to be difficult to properly form an even numberlength mark and an odd number length mark with the same division numberm only by the above-mentioned correction of β₁ and β_(m−1).

Therefore, the present inventors have conducted a further study. As aresult, it has been found that in order to properly carry out highvelocity recording as mentioned above, it is important to firstlycorrect the length of α_(m)T to obtain α_(m)′T rather than carry out theabove-mentioned correction of β₁ and β_(m−1) at the time of forming anodd number length mark.

According to the study of the present inventors, it has been found thatwhile setting β₁=β₁′ and β_(m−1)=β_(m−1)′, firstly, α_(m) is correctedto obtain Δ_(m)′ without carrying out correction of β₁ and β_(m−1)between an even number mark and an odd number mark, even in highvelocity recording, recording marks having relatively good quality canbe formed. However, at the same time, it has been found also that it isstill insufficient to correct the above α_(m) to obtain α_(m)′ in orderto certainly obtain good recording characteristics in high velocityrecording.

Thus, in the present invention, in addition to the above-mentionedcorrection of the length of α_(m)T (α_(m)≠α_(m)′), at least one of β₁T,β_(m−1)T and β_(m)T is corrected, whereby it will be possible tocertainly carry out good high velocity recording. Particularly, goodrecording can be carried out within a wide linear velocity range as inthe after-mentioned CAV or P-CAV recording.

In a conventional 2T base recording pulse division method, if thedifference 1T between an even number length mark and an odd numberlength mark with the same division number m is corrected solely byoff-pulse sections β₁T and β_(m−1)T, the sum of recording pulse sectionsΣα_(i)T (Σα_(i)′T) imparted to form the above-mentioned even numberlength and odd number length marks will be the same for the even numberlength mark and the odd number length mark. Further, in the presentinvention, primarily, a case is supposed wherein writing power Pw isconstant in recording pulse sections to form one record mark (namely,writing power Pw is set to be constant in the respective sections fromα₁T to α_(m)T) Accordingly, Σα_(i)T (Σα_(i)′T) being the same for aneven number length mark and an odd number length mark, means that thesum of recording energies Pw (Σα_(i)T) relating to the formation of oneset of an even number mark and an odd number mark becomes to be the same(Σα_(i)T=Σα_(i)′T).

Whereas, recording devices (drives) to carry out recording on opticalrecording media usually have certain fluctuation in outputs oflaser-generating means among the individual recording devices. Thismeans that the above-mentioned writing power Pw is fluctuating among therecording devices. As a result of an extensive study by the presentinventors, it has been found that by the irradiation method forrecording energy wherein the sum of recording energies Pw(Σα_(i)T)relating to the formation of one set of an even number mark and an oddnumber mark becomes to be constant, there is a problem that due to theabove-mentioned fluctuation of Pw among the recording devices, thechange in the odd number mark length and the even number mark lengthwith the same division number m will not be the same. Namely, by anincrease or decrease ΔPw of writing power Pw due to the fluctuationamong recording device products, even if one set of even number and oddnumber mark lengths with the same m are recorded, among the recordingdevices, the above-mentioned mark lengths will deviate by ΔTmark. Here,if ΔTmark of the odd number mark is substantially the same as ΔTmark ofthe even number mark, there will be no problem, but it has been foundthat if correction of only off-pulse sections of β₁T and β_(m−1)T iscarried out by means of a 2T base recording pulse strategy as arecording method (a method wherein Pw (Σα_(i)T) is constant), due to ΔPwamong the recording devices, ΔTmark of an odd number mark length isremarkably different from ΔTmark of an even number mark.

In the conventional 1T base recording pulse division method shown inFIG. 1, every time when the mark length changed by 1T, one recordingpulse was added, and thus a rule was maintained such that if the marklength became long, the sum of recording energies was monotonouslyincreased. Accordingly, ΔTmark due to fluctuation of Pw among recordingdevices was substantially constant irrespective of an odd number or evennumber mark. However, as mentioned above, by the conventional 1T baserecording pulse division method, it is impossible to carry out highvelocity recording at a level of 24 or 32-times velocity for CD-RW or8-times velocity or 10-times velocity for RW-DVD, and it becomesessential to use a 2T base recording pulse division method to secure thelaser irradiation time and the cooling time. Accordingly, so long as the2T base recording pulse division method is employed, it becomesimportant that the above-mentioned ΔTmark is made to be substantiallyconstant between an even number mark and an odd number mark.

Therefore, the present inventors have conducted a further study of the2T base recording pulse division method to make good recording possibleeven at 24-times velocity or 32-times velocity of CD-RW or even at8-times velocity or 10-times velocity of RW-DVD. As a result, it hasbeen found that in order to make ΔTmark due to ΔPw among recordingdevices to be substantially constant between an even number mark lengthand an odd number mark length, it is effective that in the 2T baserecording pulse division method, α_(m)T is necessarily corrected betweenan even number (2m) mark and an odd number (2 m+1) mark with the samedivision number m, so that the sum of recording energies Pw(Σα_(i)T) isincreased together with the mark length. It is preferred that Σα_(i)Tincreases generally by 0.5T every time when the mark length increases by1T. Every time when m increases by 1, α_(i)T and β_(i)T will increase by1, respectively, and in such a case, usually, intermediate pulses αcTand βcT will be added. βc+αc is generally 2, hence Σα_(i)T increases by1T on average. The same division number m includes two cases of n andn+1, and if the mark length is increased by 1T from n to n+1, Σα_(i)Twill be increased generally by 0.5T.

For this purpose, as mentioned above, it is difficult to obtain a goodrecording power margin by adjusting only β₁, β_(m−1) and lengths ofother off-pulse sections to adjust a mark length of 1T as the differencebetween an even number mark and an odd number mark, with the same m.

On the other hand, with respect to a question of which length ofrecording pulses α_(i)T should be adjusted, it is most preferred toadjust the length of the last α₁T i.e. α_(m)T with the same m, in orderto provide the same function as that every time when m increases ordecreases, the last α_(i)T will increase by one.

Further, by a study by the present inventors, it has been foundeffective to correct, in addition to α_(m)T, at least one of β₁T,β_(m−1)T and β_(m)T, in order to obtain low jitter at the mark ends,together with correction of the mark length by 1T. Further, according toa study by the present inventors, it has been found also that whenα_(m)′=α_(m)+Δ_(m), Δ_(m) is preferably within a range of 0<Δ_(m)≦1rather than being accurately 1. Further, it has been found that Δ₁,Δ_(m−1) and Δ_(m)′ are preferably at most 1, also when β₁′=β₁+Δ₁,β_(m−1)′=Δ_(m−1)+Δ_(m−1) and β_(m)′=β_(m)+Δ_(m)′.

In this way, a difference of mark length T will be imparted dependingupon whether n is an even number or an odd number with the same divisionnumber m, and specifically, the following two methods may be mentioned.

Recording Pulse Division Method II

This recording pulse division method is a method wherein in the“Recording pulse division method I”, when m is 3 or more, with the samedivision number m, for a record mark of n=2m and a record mark ofn=2m+1, α_(m)≠α_(m)′and β₁≠β₁′, and at least one set selected from(T_(d1), T_(d1)′), (α₁ and α₁′), (β_(m−1) and β_(m−1)′) and (β_(m) andβ_(m)′) takes different values.

Specifically, with the same division number m, (β_(m−1) ′+α_(m)′+β_(m)′)in a case where n is an odd number is made larger than(β_(m−1)+α_(m)+β_(m)) in a case where n is an even number, and at thesame time, β₁′ in a case where n is an odd number is preferably made tobe larger than β₁ in the case where n is an even number.

Namely, α_(m)′=α_(m)+Δ_(m), and at the same time, β₁′>β₁ and β₁′=β₁+Δ₁.Here, Δ_(m) is larger than 0, preferably at least 0.2 and on the otherhand, at most 1, preferably at most 0.7, more preferably at most 0.6.Further, Δ₁ is larger than 0, preferably at least 0.2 and on the otherhand, at most 1, preferably at most 0.7, more preferably at most 0.6.

More specifically, it is preferred that β₁′=β₁+Δ₁ (where 0<Δ₁≦1),β_(m−1)′+α_(m)′β_(m−1)+Δ_(m−1)+Δ_(m)+Δ_(m)=β_(m−1)+α_(m)+Δ_(mm)(Δ_(mm)=0.2 to 1). The upper limit of the value for Δ₁ and Δ_(mm) ispreferably at most 1, and Δ₁ is particularly preferably made to be avalue of from 0.2 to 0.7, more preferably from 0.3 to 0.6. Among them,in β_(m−1)′=β_(m−1)+Δ_(m−1) and α_(m)′=α_(m)+Δ_(m), 0 to 1 is allocatedto each of Δ_(m−1) and Δ_(m), but the upper limits of Δ_(m−1) and Δ_(m)are preferably at most 0.7, more preferably at most 0.6. Further,Δ_(m−1)+Δ_(m)+Δ_(m)′ is preferably from 0.2 to 1.2.

Particularly when m is 3 or more, it is preferred that T_(d1)′=T_(d1),α₁′=α₁′, β₁′=β₁+Δ₁ (0<Δ₁≦1), β_(m−1)′=β_(m−1)+Δ_(m−1) (Δ_(m−1)=0 to 1),α_(m)′=α_(m)+Δ_(m) (0<Δ_(m)≦1), Δ_(mm)=Δ_(m−1)+Δ_(m), and 0<Δ_(mm)≦1.Here, it is preferred that Δ₁ and Δ_(mm) are made to have a value offrom 0.2 to 0.7. It is preferred that Δ_(m−1) is made to have a value offrom 0 to 0.7, and Δ_(m) is made to have a value of from 0.2 to 0.7.

To simplify the pulse-generating circuit, it is preferred that β₁+α₂ andβ_(m−1)+α_(m) take a value within a range of from 1.7 to 2.3, andparticularly preferably, β₁+α₂=2, and β_(m−1)+α_(m)=2.

Further, it is preferred that α_(m)=αc. Further, it is preferred thatα₁=α₁′, and further, α₁=α₁′=αc, with a view to reducing the number ofvariable parameters.

Here, when m=2 (n=4 or 5), m−1=1, hence section (β₁+α₂)T may be regardedas section (β_(m−1)+α_(m))T. In such a case, (β₁′+α₂′)T of 5T mark ismade longer by about 1T than (β₁+α₂)T of 4T mark. More specifically, itis preferred that α₁, α₁′, α₂, α₂′, β₂ and β₂′ are, respectively, madeto be equal to α₁, α₁′, α_(m), α_(m)′, β_(m) and β_(m)′ in a case wherem is 3 or more, and β₁ made to be equal to either β₁ or β_(m−1) at any min a case where m is 3 or more, and β₁′ is made to be equal to eitherβ₁′ or β_(m−1)′ at any m in a case where m is 3 or more. It is preferredthat the respective values of α₁, α₁′, α₂, α₂′, β₂ and β₂′ when m=2 aremade to be equal to α₁, α₁′, α₃, α₃′, β₃ and β₃′ in a case where m=3, β₁is made to be equal to β₁ or β₂ in a case where m=3, and β₁′ is made tobe equal to either β₁′ or β₂′ in a case where m=3 or more. Particularlypreferably, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in a case where m=2are, respectively, made to be equal to α₁, α₁′, β₂, β₂′, α₃, α₃′, β₃ andβ₃′ in a case where m is 3.

However, in any case relating to m=2, with respect to β₂′, fineadjustment is further allowable within a range of ±0.5. Thus, when n=4or 5, those capable of taking values different from a case where m is 3or more, are three parameters of T_(d1), T_(d1)′ and β₂′

Further, when m=1 (n=3), recording light irradiation comprising a pairof writing power irradiation section α₁′T and bias power irradiationsection β₁′T, is carried out. In such a case, it is preferred that α₁′is made to be larger by from about 0.1 to 1.5 than α₁′ in a case where mis 3 or more, and β₁′ is made to be smaller than β₁′ and larger thanβ_(m) and β_(m)′ in a case where m is 3 or more. Otherwise, it is alsopreferred that α₁′ is made to be from 1 to 2 times of α₁′ in a casewhere m is 3 or more.

As another specific method,

Recording Pulse Division Method III

This recording pulse division method is one wherein in the “Recordingpulse division method I”, when m is 3 or more, with the same divisionnumber m, for a record mark of n=2m and a record mark of n=2m+1,α_(m)≠α_(m)′, T_(d1)=T_(d1)′, α₁=α₁′ and β₁=β₁′, and at least one setselected from (β_(m−1), and β_(m−1)′) and (β_(m) and β_(m)′) takesdifferent values. Already in the “Recording pulse division method I”,β_(i−1)+α_(i)=β_(i−1)′+α_(i)′=β_(c)+α_(c) (i=2 to m−1), and accordingly,by setting T_(d1)=T_(d1)′, α₁=α₁′ and β₁=β₁′, it is possible tosynchronize all recording pulse and off-pulse sections up to the starttime of the off-pulse section β_(m−1)T and β_(m−1)′T with respect to aneven number mark and an odd number mark, whereby the recordingpulse-generating circuit can be simplified to a large extent.

Namely, when m is 3 or more, with the same division number m, about 1 isadded to (β_(m−1)+α_(m)+β_(m)) in a case where n is an even number toobtain (β_(m−1)′+α_(m)′+β_(m)′) in a case where n is an odd number.About 1 to be added to the above (β_(m−1)+α_(m)+β_(m)) is preferably avalue within a range of from 0.5 to 1.5, more preferably a value withina range of from 0.5 to 1.2. Among them, to β_(m−1) and β_(m), a value ofat least 0 and at most 1 is given and to α_(m), a value larger than 0and at most 1 will be given, but it is more preferred that the upperlimits of the values given to β_(m−1) and α_(m) are at most 0.6. If itis attempted to carry out correction of a mark length of 1T solely byα_(m), the rear end jitter is likely to be high, and at least eitherβ_(m−1) or β_(m) is corrected together with α_(m). Here, as explained inthe Recording pulse division method I, α₂′=α₂=αc, hence β₁′+α₂′=β₁+α₂.

Namely, when m is 3 or more, it is preferred thatβ_(m−1)′=β_(m−1)+Δ_(m−1) (Δ_(m−1)=0 to 1), α_(m)′=α_(m)+Δ_(m)(0<Δ_(m)≦1), β_(m)=β_(m)+Δ_(m)′ (Δ_(m)′=0 to 1) andΔ_(m)+Δ_(m)′=Δ_(m−1)+Δ_(m)+Δ_(m)′=0.5 to 1.5, more preferably 0.5 to1.2.

β₁+α₂=β₁′+α₂′ and β_(m−1)+α_(m) preferably take values within a range offrom 1.5 to 2.5, as mentioned above, and more preferably take valueswithin a range of from 1.7 to 2.3. It is particularly preferred thatβ₁+α₂=2, and β_(m−1)+α_(m)=2.

Here, when m=2 (n=4 or 5), m−1=1, and accordingly, section (β₁+α₂)T maybe regarded as section (β_(m−1)+α_(m))T. In such a case, (β₁+α₂)T of 5Tmark is made longer by about 1T than (β₁+α₂)T of 4T mark. Morespecifically, it is preferred that α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′are, respectively, made to be equal to α₁, α₁′, β_(m−1), β_(m−1)′,α_(m), α_(m)′, β_(m) and β_(m)′ at any m which is 3 or more.

However, with respect to α₂, α₂′, β₂ and β₂′ where m=2, fine adjustmentof the value may further be carried out within a range of ±0.2, butnecessity for such adjustment is small. Particularly preferred is thatα₁, α₁′, β₁′, α₂, α₂′, β₂ and β₂′ where m=2, are made to be equal to α₁,α₁′, β₂, β₂′, α₃, α₃′, β₃ and β₃′ where m=3, respectively.

Further, when m=1 (n=3), again, recording laser beam irradiationcomprising a pair of writing power irradiation section α₁′T and biaspower irradiation section β₁′T, is carried out. In such a case, α₁′ ispreferably made to be larger by from about 0.1 to 1.5 than α₁′ where mis 3 or more. Otherwise, α₁′ is preferably made to be from 1 to 2 timesof α₁′ where m is 3 or more.

As described above, in the “recording pulse division method III”, when mis 3 or more, β₁′=β₁, and about 1 is added to (β_(m−1)+α_(m)+β_(m)) inthe case where n is an even number to obtain (β_(m−1)′+α_(m)′+β_(m)′) inthe case where n is an odd number, with the same division number m. Inorder to add the above 1, in addition to setting α₁′=α_(m)+Δ_(m), threecases are conceivable i.e. a case where β_(m−1)′=β_(m−1)+Δ_(m−1), a casewhere β_(m)=β_(m)+Δ_(m)′ and a case β_(m−1)′=β_(m−1)+Δ_(m−1) andβ_(m)=β_(m)+Δ_(m)′. Among them, in a case where recording is carried outat a linear velocity slower than the upper limit of the recordablelinear speed, it is preferred that firstly β_(m)=β_(m)+Δ_(m)′ is set sothat correction of β_(m) is given priority over correction of β_(m−1).The reason will be given below.

Namely, when recording is carried out on a recording medium of thepresent invention at a linear velocity lower than the upper limit of theoverwritable linear velocity, a correction of α_(m)′>α_(m) presents asubstantial influence over the cooling process of the rear end of amark. Accordingly, the correction value Δ_(m)′ for β_(m) is preferablycorrected to be β_(m)′=β_(m)+Δ_(m)′ (Δ_(m)′=0 to 1). For example, thisapplies to a case where recording is carried out at less than 24-timesvelocity on a CD-RW medium of the present invention overwritable at24-times velocity or a case where recording is carried out at less than8-times velocity on a RW-DVD medium of the present inventionoverwritable at 8-times velocity, and is useful in a case where theafter-mentioned CAV or P-CAV recording is carried out. In such a case,it is preferred to give priority to Δ_(m)′>0 over Δ_(m−1).

In the recording pulse division methods (I), (II) and (III), α_(i) andβ_(i) can, respectively, be optimized with respect to the respectivemark lengths, but for simplification of the pulse-generating circuit,they are preferably made to have constant values as far as possible.

Firstly, with respect to intermediate recording pulses present in a casewhere m is 3 or more, it is preferred that α_(i) and α_(i)′ (i=2 to m−1)are made to be constant with a value αc irrespective of i and n. Then,the forefront pulse parameters α₁ and α₁′ can be made to have constantvalues irrespective of an even number length mark or an odd numberlength mark with m being at least 2, or at least with m being at least3. That is α₁′=α₁, and α₁ is preferably made to have a constant valueirrespective of m. In such a case, again, it is preferred thatT_(d1)=T_(d1)′ is also constant at least with m being at least 3.

With respect to α_(m) and α_(m)′, they are different for an even numberlength mark and an odd number length mark with the same m, but with mbeing at least 3, more preferably with m being at least 2, irrespectiveof m, β_(m) for an even number length mark is made to be constant, andα_(m)′ for an odd number length mark can be made to be constant. And, itis preferred that also α_(m) for an even number length mark is made tobe αc.

In addition to the foregoing, in the recording pulse division method(II), when m is at least 3, more preferably when m is at least 2, Δ₁,Δ_(m−1) and Δ_(m) are, respectively, made to be constant. Accordingly,Δ_(mm)=Δ_(m−1)+Δ_(m) also becomes constant.

As described in the foregoing, if parameters not depending on m aretaken into consideration, in the case of RW-DVD, even if a case wheren=14 is to be added, it is required only to insert two pairs of αcT andβcT, whereby the number of independent parameters is considered to bethe same as in the case of CD-RW.

In summarizing the foregoing, the recording pulse division method (II)will be the following more simplified recording pulse division method.

Namely, with m being 3 or more (i.e. n being 6 or more), relations ofT_(d1)′=T_(d1), α₁′=α₁, β₁+α₂=1.5 to 2.5, β_(m−1)+α_(m)=1.5 to 2.5,β₁′=β₁+Δ₁ (0<Δ₁≦1), β_(m−1)=β_(m−1)+Δ_(m−1) (Δ_(m−1)=0 to 1),α_(m)′=α_(m)+Δ_(m)(0<Δ_(m)≦1), Δ_(mm)=Δ_(m−1)+Δ_(m)=0.2 to 1, andβ_(m)′=β_(m)+Δ_(m)′ (Δ_(m)′=0 to 1) are satisfied, and T_(d1), α₁, β₁,Δ₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m), β_(m) and Δ_(m)′ can be madeconstant irrespective of m when m is 3 or more.

Here, by setting (T_(d1)+α₁)T=(T_(d1)′+α₁′)′T=2T especially with m being3 or more, it is possible to synchronize the falling of each recordingpulse α_(i)T with the clock period especially for an even number lengthmark, whereby the circuit can further be simplified. Here, for a markwherein m is 3 or more (n is 6 or more), the following recording pulsedivision method (II-A) can be defined by 11 independent parameters of(T_(d1), α_(i), β₁, Δ₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m), β_(m) andΔ_(m)′).

Namely, the recording pulse division method (II-A) is a recording methodfor a rewritable optical recording medium wherein:

between record marks, a laser beam having an erasing power Pe capable ofcrystallizing an amorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 2), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, provided thatΣ_(i)(α_(i)+β_(i))=n−j and for a record mark of n=2m+1 (where m is aninteger of at least 2), of which the time length (n−k)T (where k is areal number of from −2.0 to 2.0) is divided into m sections of α_(i)′Tand β_(i)′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . . , α_(m)′T andβ_(m)′T, provided that Σ_(i)(α_(i)′+β_(i)′)=n−k, a laser beam having aconstant writing power Pw (provided that Pe/Pw=0.2 to 0.6) sufficient tomelt the recording layer is applied within a time of α_(i)T and α_(i)′T(where i is an integer of from 1 to m), and a laser beam having a biaspower Pb of Pb≦0.2Pe is applied within a time of β_(i)T and β_(i)′T(where i is an integer of from 1 to m); and

when n=2m (m is at least 3), when the start time for nT mark isrepresented by T₀, after a delay time T_(d1)T from T₀, α₁T, β₁T andα₂T=αcT are generated in this order, then, while maintaining generallyperiod 2T, β_(i−1)T=βcT and α_(i)T=αcT (i=3 to m−1, and αc and βc=2−αcare constant irrespective of i), are alternately generated in thisorder, and then, β_(m−1)T, α_(m)T and β_(m)T are generated in thisorder, and

when n=2m+1 (m is at least 3), when the start time for nT mark isrepresented by T₀, after a delay time T_(d1)′T from T₀, α₁′T, β₁′T andα₂′T=αcT are generated in this order, then, while maintaining generallyperiod 2T, βcT=β_(i−1)′T and αcT=α_(i)′T (i=3 to m−1) are alternatelygenerated in this order, and then α_(m)′T and β_(m)′T are generated inthis order after β_(m−1)′T, and further

when m is at least 3, with the same division number m, the relations ofT_(d1)′=T_(d1), α₁=α₁′, β₁′=β₁+Δ₁ (0<Δ₁≦1), β_(m−1) ′=β_(m−1)+Δ_(m−1)(Δ_(m−1)=0 to 1), α_(m)′=αc+Δ_(m) (0<Δ_(m)≦1), Δ_(mm)=Δ_(m−1)+Δ_(m),0<Δ_(mm)≦1, β_(m)′=β_(m)+Δ_(m)′ (Δ_(m)′=0 to 1), are satisfied, andT_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m), β_(m) and Δ_(m)′are constant irrespective of m.

Here, when m=2, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are preferablymade to be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) andβ_(m)′ in the case of m=3, respectively (provided that β₂′ may furtherbe adjustable within a range of ±0.5).

The above-mentioned recording methods CD1-1 and 2-1 and DVD1-1 and 2-1correspond to such recording pulse division method (II-A), wherein theranges and relative degrees of various parameters are more restrictivelydefined.

In the above recording pulse division method (II-A), “maintaininggenerally period 2T” represents (β_(i−1)+α₁)T=2T (i=2 to m) and(β_(i−1)′+α_(i)′)T=2T (i=3 to m−1) and not only means to allow aninevitable deviation from 2T to realize an electronic circuit but alsomeans to allow fine adjustment within a range of ±0.5T with respect to(β₁+α₂)T and (β_(m−1)+α_(m))T.

Thus, with respect to mark lengths where m is 3 or more (n is 6 ormore), the recording pulse division method can be defined by elevenindependent parameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1), α_(m),Δ_(m), β_(m) and Δ_(m)′), and further, if T_(d1)′, α₁′ and β₁′ (total of3 parameters) where n=3 and parameters of T_(d1), T_(d1)′, α₂′ and β₁′(total of 4 parameters) where m=2 (n=4 or 5) are defined, a recordingpulse division method for forming all mark lengths of from 3 to 11 willbe fixed. Further, if Pw and Pb take constant power levels at allsections, they may together with Pe define three types of writing powerlevel values, and thus total of 21 independent parameters i.e.11+3+4+3=21 may be defined.

Here, in the pulse division method (II-1), in order to more simplifydesigning of the control circuit (electronic circuit) to control laserbeams (pulsed beams) for recording pulses and off-pulses of therecording pulse strategy, it is preferred to set that at least oneformula among T_(d1)+α₁=2, α₁=αc, β₁+α₂=2, β_(m−1)+α_(m)=2 and α_(m)=αc,is satisfied when m is at least 3.

When m is 3 or more (namely n=6 or more), it is preferred to setT_(d1)+α₁=2, β₁+α₂32 2 and β_(m−1)+α_(m)=2, whereby the falling of eachrecording pulse α_(i)T where i=1 to m can be synchronized to the clockperiod, and the circuit can be further simplified. In such a case,T_(d1)′+α₁′=2. Further, it is preferred to set β₁′+α₂′=2.5 i.e.β₁′=β₁+0.5, whereby the falling of each recording pulse α_(i)′T wherei=1 to m−1 can be synchronized to a ½ period of the clock period; thenumber of independent parameters can be reduced to a large extent, andthe circuit can be further simplified.

Independent parameters in this case include three parameters of therecording power levels, three parameters of T_(d1)′, α₁′, and β₁′ wheren=3, four parameters of T_(d1), T_(d1)′, α₂′ and β₂ ′ where n=4 or 5 andeight parameters of (α₁, Δ₁, αc, Δ_(m−1), α_(m), Δ_(m), β_(m) andΔ_(m)′) where n is 6 or more in a total of 3+3+4+8=18 parameters,whereby determination of the parameters can be simplified. It is morepreferred to set T_(d1)+α₁=T_(d1)′+α₁=2 where m is 2 or more (n is 4 ormore). In such a case, two parameters of T_(d1) and T_(d1)′ where n=4 or5 will become non-independent, whereby the number of independentparameters will be 16. It is further preferred to set α_(m)=αc or α₁=αcwhere m is 3 or more, whereby the number of independent parameters canfurther be reduced. If α_(m)=α₁=αc, the number of independent parameterswill be 14.

Namely, it is preferred that like in the case of m=3 or more, also whenm=2, at least one of T_(d1)+α₁=T_(d1)′+α₁′=2, α₁=α₁′, β₁+α₂=2 and α₂=αcis satisfied.

Further, if, irrespective of whether α_(m), α₁ and αc are equal or not,ratios of α₁/αc and α_(m)/αc, or differences of α₁−αc and α_(m)−αc takepredetermined values, α₁ and α_(m) will be univocally determined once αcis determined, whereby the number of parameters can be reduced. In sucha case, specifically, the ratios of α₁/αc and α_(m)/αc preferably take avalue of 1 to 2. Further, the ratios of α₁/αc and α_(m)/αc may bemutually different so long as they are values within this range.

Further, if α₁>αc, there may be a case where the power required forrecording can be reduced, and in such a case, it is advisable topositively differentiate α₁ and αc.

Further, α₁′ where n=3 may be set to be equal to α₁ in a case where n=4or more; or α₁′ where n=3, and α_(i) or αc where n is 4 or more, may beset to have a constant ratio or difference.

On the other hand, in the recording pulse division method (III), it ispreferred to employ the following simplified recording pulse divisionmethod. Namely, it is preferred that when m is at least 3 i.e. n is atleast 6, the relations of T_(d1)′=T_(d1), α₁′=α₁, β₁′=β₁, β₁+α₂=1.5 to2.5, β_(m−1)+α_(m)=1.5 to 2.5, β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 1), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)=≦1),Δ_(mm)+Δ_(m)′=Δ_(m−1)+Δ_(m)+Δ_(m)′=0.5 to 1.5 and β_(m)′=β_(m)+Δ_(m)′(where Δ_(m)′=0 to 1), are satisfied, and when m is at least 3, T_(d1)′,α₁, β₁ and αc are constant irrespective of m. Further, it is preferredthat Δ_(m−1), Δ_(m−1), α_(m), β_(m) and Δ_(m)′ are also set to beconstant when m is at least 3. Δ_(m) may take two values of Δ_(m1) andΔ_(m2), but preferably Δ_(m1)=Δ_(m2). Each of Δ_(m−1) and Δ_(m)′ is morepreferably from 0 to 0.7, particularly preferably from 0 to 0.6. Δ_(m)is preferably larger than 0 and at most 0.7, more preferably larger than0 and at most 0.6.

The following recording pulse division method (III-A) may be defined.

That is,

Recording Pulse Division Method (III-A)

This is a recording method for a rewritable optical recording mediumwherein:

between record marks, a laser beam having an erasing power Pe capable ofcrystallizing an amorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 2), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, provided thatΣ_(i)(α_(i)+β_(i))=n−j and for a record mark of n=2m+1 (where m is aninteger of at least 2), of which the time length (n−k)T (where k is areal number of from −2.0 to 2.0) is divided into m sections of α_(i)′Tand β_(i)′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . . , α_(m)′T andβ_(m)′T, provided that Σ_(i)(α_(i)′+β_(i)′)=n−k, a laser beam having aconstant writing power Pw (provided that Pe/Pw=0.2 to 0.6) sufficient tomelt the recording layer is applied within a time of α_(i)T and α_(i)′T(where i is an integer of from 1 to m), and a laser beam having a biaspower Pb of Pb≦0.2Pe is applied within a time of β_(i)T and β_(i)′T(where i is an integer of from 1 to m); and

when n=2m (m is at least 3), when the start time for nT mark isrepresented by T₀, after a delay time T_(d1)T from T₀, α₁T, β₁T andα₂T=αcT are generated in this order, then, while maintaining generallyperiod 2T, β_(i−1)T=βcT and α_(i)T=αcT (i=3 to m−1, and αc and βc=2−αcare constant irrespective of i), are alternately generated in thisorder, and then, β_(m−1)T, α_(m)T and β_(m)T are generated in thisorder, and

when n=2m+1 (m is at least 3), when the start time for nT mark isrepresented by T₀, after a delay time T_(d1)′T from T₀, α₁′T, β₁′T andα₂′T=αcT are generated in this order, then, while maintaining generallyperiod 2T, βcT=β_(i−1)′T and αcT=α_(i)′T (i=3 to m−1) are alternatelygenerated in this order, and then α_(m)′T and β_(m)′T are generated inthis order after β_(m−1)′T, and further

when m is at least 3, with the same division number m, the relations ofT_(d1)′=T_(d1), α₁=α₁′, β₁′=β₁, β₁+α₂=1.5 to 2.5, β_(m−1)+α_(m)=1.5 to2.5, β_(m−1)′=β_(m−1)+Δ_(m−1) (Δ_(m−1)=0 to 1), α_(m)′=α_(m)+Δ_(m)(0<Δ_(m)=1), Δ_(m−1)+Δ_(m)+Δ_(m)′=0.5 to 1.5, β_(m)′=β_(m)+Δ_(m)′(Δ_(m)′=0 to 1), are satisfied, and T_(d1), α₁, β₁, αc, β_(m−1),Δ_(m−1), α_(m), β_(m) and Δ_(m)′ are constant irrespective of m(provided that Δ_(m) may take two values of Δ_(m1) and Δ_(m2) dependingon m).

Here, when m=2, like in the recording pulse division method (III), α₁,α₁′, β₁, β₁, α₂, α₂′, β₂ and β₂′ are preferably made to be equal to α₁,α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) and β_(m)′ in the case ofm=3, respectively.

In the above recording pulse division method (III-A), “maintaininggenerally period 2T” represents (β_(i−1)+α₁)T=2T (i=2 to m) and(β_(i−1)′+α_(i)′)T=2T (i=3 to m−1) and not only means to allow aninevitable deviation from 2T to realize an electronic circuit but alsomeans to allow fine adjustment within a range of ±0.5T with respect to(β₁+α₂)T and (β_(m−1)+α_(m))T.

Thus, with respect to mark lengths where m is 3 or more (n is 6 ormore), the recording pulse division method can be defined by elevenindependent parameters (T_(d1), α₁, β₁, αc, β_(m−1), Δ_(m−1), α_(m),Δ_(m1), Δ_(m2), β_(m) and Δ_(m)′) and further, if T_(d1) or T_(d1)′(total of 3 parameters) each at n=3, 4 and 5 and parameters of α₁′ andβ₁′ (total of 2 parameters) where m=3 are defined, a recording pulsedivision method for forming all mark lengths of from 3 to 11 will befixed. Further, if Pw and Pb take constant power levels at all sections,they may together with Pe define three types of writing power levelvalues, and thus total of 19 independent parameters i.e. 11+3+2+3=19 maybe defined.

The above-mentioned recording methods CD1-2 and 2-2 and DVD1-2correspond to such recording pulse division method (III-A), wherein theranges and relative degrees of various parameters are more restrictivelydefined.

Here, in the pulse division method (III-1), in order to more simplifydesigning of the control circuit (electronic circuit) to control laserbeams (pulsed beams) for recording pulses and off-pulses of therecording pulse strategy, it is preferred to carry out the followingsettings.

Firstly, Δ_(m)=Δ_(m1)=Δ_(m2) is set when m is at least 3.

Secondly, it is so set that at least one formula among T_(d1)+α₁=2,α₁=αc, β₁+α₂=2, β_(m−1)+α_(m)=2 and α_(m)=αc, is satisfied when m is atleast 3.

Particularly when m is 3 or more, it is preferred to set T_(d1)+α₁=2 andβ₁+α₂=2, whereby the falling of each recording pulse α_(i)T and α_(i)′Twhere i=1 to m−1 can be synchronized to the clock period; the circuitcan be further simplified; and the number of independent parameters canbe reduced to a large extent. Further, β₁=β₁′ and α₂=α₂′=αc, thus, ifβ₁+α₂′=2, β₁′+α₂′=2 will be satisfied. Likewise, T_(d1)=T_(d1)′ andα₁=α₁′, thus, if T_(d1)+α₁=2, T_(d1)1′+α₁′=2 will be satisfied.

Independent parameters in this case include three parameters of therecording power levels, three parameters of T_(d1)′, α₁′, and β₁′ wheren=3, two parameters of T_(d1) and T_(d1)′ where n=4 or 5 and eightparameters of (α₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m), β_(m) and Δ_(m)′)where m is 3 or more in a total of 3+3+2+8=16 parameters, wherebydetermination of the parameters can be simplified. It is furtherpreferred to set β_(m−1)+α_(m)=2 and α_(m)=αc, whereby the number ofparameters can further be reduced by two to 14.

Or, if ratios of α₁/αc and α_(m)/αc, or differences of α₁−αc andα_(m)-αc take predetermined values, α₁ and α_(m) will be univocallydetermined once αc is determined, whereby the number of parameters canagain be reduced, such being preferred. In such a case, specifically,the ratios of α₁/αc and α_(m)/αc preferably take a value of 1 to 2.Further, the ratios of α₁/αc and α_(m)/αc may be mutually different solong as they are values within this range.

Further, if α₁>αc, there may be a case where the power required forrecording can be reduced, and in such a case, it is advisable topositively differentiate a and αc.

Further, α₁′ where n=3 may be set to be equal to α₁ in a case where n=4or more; or α₁′ where n=3, and α₁ or αc where n is 4 or more, may be setto have a constant ratio or difference.

It is more preferred to set T_(d1)+α₁=2 for all m which is 2 or more. Insuch a case, two parameters of T_(d1) and T_(d1)′ where n=4 or 5 willbecome non-independent, whereby the number of independent parameterswill be 12.

Namely, it is preferred that like in the case of m=3 or more, also whenm=2, at least one of T_(d1)+α₁=T_(d1)′+α₁′=2, α₁=α₁′, β₁+α₂=2 and α₂=αcis satisfied.

Here, as the simplest recording pulse division method, a recording pulsedivision method (III-B) which can be regulated only by 12 independentparameters (α₁, αc, Δ_(m−1), Δ_(m), β_(m) and Δ_(m)′ where n is at least4, T_(d1)′, α₁′ and β₁′ where n=3, and Pw, Pe and Pb), will be definedas follows.

That is,

Recording Pulse Division Method (III-B)

This is a recording method for a rewritable optical recording mediumwherein:

between record marks, a laser beam having an erasing power Pe capable ofcrystallizing an amorphous phase is applied, and

for a record mark of n=2m (where m is an integer of at least 2), ofwhich the time length (n−j)T (where j is a real number of from −2.0 to2.0) is divided into m sections of α_(i)T and β_(i)T comprising α₁T,β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T, provided thatΣ_(i)(α_(i)+β_(i))=n−j and for a record mark of n=2m+1 (where m is aninteger of at least 2), of which the time length (n−k)T (where k is areal number of from −2.0 to 2.0) is divided into m sections of α_(i)′Tand β₁′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . . , α_(m)′T and β_(m)′T,provided that Σ_(i)(α_(i)′+β_(i)′)=n−k, a laser beam having a constantwriting power Pw (provided that Pe/Pw=0.2 to 0.6) sufficient to melt therecording layer is applied within a time of α_(i)T and α_(i)′T (where iis an integer of from 1 to m), and a laser beam having a bias power Pbof Pb≦0.2Pe is applied within a time of β_(i)T and β_(i)′T (where i isan integer of from 1 to m); and

when n=2m (m is at least 3), when the start time for nT mark isrepresented by T₀, after a delay time T_(d1)T from T₀, α₁T is generated,then, while maintaining generally period 2T, βcT=β_(i−1)T and αcT=α_(i)T(i=2 to m, and αc and βc=2−αc are constant irrespective of i), arealternately generated in this order, and then, β_(m)T is generated inthis order, and

when n=2m+1 (m is at least 3), when the start time for nT mark isrepresented by T₀, after a delay time T_(d1)′T from T₀, α₁′T isgenerated, then, while maintaining generally period 2T, βcT=β_(i−1)′Tand αcT=α_(i)′T(i=2 to m−1) are alternately generated in this order, andthen α_(m)′T and β_(m)′T are generated in this order after β_(m−1)′T,and further

when m is at least 3, with the same division number m, the relations ofT_(d1)′=T_(d1), T_(d1)+α₁=2, α₁=α₁′, β_(m−1)′=β_(m−1)+Δ_(m−1) (Δ_(m−1)=0to 1), α_(m)′=αc+Δ_(m) (0<Δ_(m)≦1), Δ_(m−1)=Δ_(m)Δ_(m)′=0.5 to 1.5,β_(m)′=β_(m)+Δm′ and Δ_(m)′=0 to 1, are satisfied, and αc, Δ_(m−1),Δ_(m), β_(m) and Δ_(m)′ are constant irrespective of m.

Here, when m=2, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are made to beequal to α₁, α₁′, β₂(=βc), β₂′(=βc+Δ_(m−1)), α₃(=αc), α₃′(=αc+Δ_(m)), β₃and β₃′=(β₃+Δ_(m)′) in the case of m=3, respectively.

Here, in the recording pulse division method (III-B), it is morepreferred to set α₁=α₁′=αc where m is at least 3, further where m is atleast 2. Further, especially at about 20-times velocity to 32-timesvelocity of CD-RW (at 6-times velocity to 12-times velocity of RW-DVD),it is preferred to set Δ_(m)′=0, i.e. when m is at least 3,β_(m)′=β_(m). Further, it is more preferred to set β_(m)′=β_(m) when mis at least 2.

Further, in recording pulse division method (III-A) or (III-B), it ispossible to set either Δ_(m−1) or Δ_(m) ′ to be zero or to setΔ_(m−1)=Δ_(m) and thereby to further reduce the number of parameters. Itis a feature of the recording medium of the present invention that goodcharacteristics can be obtained even if the number of parameters isreduced like this. And, among recording media of the present invention,an optical recording medium employing a GeSb type recording layer showsparticularly distinct tendency for such good characteristics. Namely, byusing an optical recording medium employing a GeSb type recording layer,the effect of the present invention can be most effectively obtainedsuch that good high velocity recording characteristics can be realizedby a simple recording pulse division method.

“Recording method CD1-3” or “Recording method DVD1-3” corresponds tothis recording pulse division method (III-B) wherein α₁=α₁′=αc, and inorder to define characteristics of a recording medium within specificranges and to secure recording interchangeability among a plurality ofdrives, the ranges of eleven independent parameters are particularlyrestrictively employed.

The above-described recording pulse division methods (III), (III-A) and(III-B) are most preferred in that the number of independent parametersis small, and it is possible to synchronize the falling of α_(i)T withini=1 to m and the falling of α_(i)′T within i=1 to m−1 to period 2T.Referring to FIG. 5, by (III-B), recording of all mark lengths of n=3 to11 will be possible by combining four types of gates G1 to G4 in a casewhere middle divided pulses are present as in the case where m is atleast 3, by combining G1, G3 and G4 in the case where m=2 and by usingG3 and G4 in the case where n=3 (m=1). It is thereby possible toconstitute the system solely by a circuit wherein gates G1 and G2 aresynchronized to period 2T without requiring an additional delay circuit,whereby a pulse-generating circuit can be very simply constituted.Further, G1 and G3 to generate α₁ and α_(m), are independent, andaccordingly, α₁ and α_(m) can be made to be values different from αc bya combination of the same gate circuits.

Thus, the recording pulse division methods (III), (III-A) and (III-B)can be realized by a simple circuit which can readily be synchronizedwith the reference clock period, as compared with any one of therecording methods specifically disclosed in JP-A-2002-331936. Especiallythe recording pulse division method (III-B) has a merit that goodrecording characteristics can be provided, even though the number ofindependent parameters is as small as 12.

The number of independent parameters being small means simplification ofthe recording pulse-generating circuit. Further, it is preferred thatsome or all of the above-mentioned independent parameters in the optimumrecording pulse division method are preliminarily written in therewritable optical recording medium, in a combination of the rewritableoptical recording medium proposed by the present invention with acertain specific drive for recording, so that such parameter informationis read out by the drive to generate optimum recording pulses to carryout recording, and in such a case, the work load to preliminarily findout the parameters to be written on the disk can be reduced, such beingpreferred.

Specifically, the recording pulse division information parameters whichare particularly desired to be written in the divided recordingpulse-generating methods (III-A) and (III-B), are the optimum writingpower Pw_(o), the optimum erasing power Pe_(o), T_(d1)′, α₁′ and β₁′where n=3 and T_(d1), α₁, αc, Δ_(m−1), Δ_(m), Δ_(m)′ and β_(m) where mis at least 3. Pw_(o) and Pe_(o) may be given as a ratio of Pe_(o) toPw_(o) (Pe_(o)/Pw_(o)).

Further, it is effective that when the disk is inserted into the drive,with respect to some or all of such parameters, the values preliminarilywritten on the disk are used as initial values, and trial writing iscarried out while letting the initial values change in their vicinities,whereupon the signals written by such trial writing are retrieved,whereby on the basis of m₁₁, the jitters, the error rate, etc., theoptimum parameters in the combination of the disk and the drive aredetermined, whereby the interchangeability can be secured.

As described in the foregoing, it will be possible to record individualamorphous mark lengths accurately at a high linear velocity whilesuppressing jitter at their edges. However, this does not necessarilymean that space length between marks are accurate, whereby jitter issuppressed. Especially in high linear velocity recording, separation ofmark jitter and space jitter is substantial, and there may be a casewhere space jitter is large on the high writing power Pw side.

In the pulse division methods (I), (II), (II-A), (III), (III-A) and(III-B), especially when n=3, it is necessary to independently determinevalues different from the parameters to be used in the pulse divisionmethod where n=4 or more. It is preferred that the recording pulse widthα₁′T where n=3 takes a value larger than each of α₁T and α₁′T in thecase where n is 4 or more. The reason for this is that it is necessaryto form α₃T mark length by a single recording pulse without the thermalstorage effect by the subsequent plurality of recording pulse train.Namely, if α₁′=α_(n=3) is too small when n=3, 3T mark length is hardlyobtainable, and if α_(n=3) is too large, the width of the mark in adirection perpendicular to the recording beam operation direction tendsto be too wide, and the mark edges tend to be hardly erased whenoverwriting is carried out, although 3T mark length may be obtained.Accordingly, in a case where α₁ and α₁′ where n is at least 4, takeconstant α₁=α₁′=α_(top), α₁′=α_(n =3) where n=3, is preferably within arange of α_(n=3)/α_(top)=1 to 2, more preferably within a range of from1 to 1.5.

Therefore, in order to further reduce 3T space length jitter, it ispreferred that in the pulse division methods (I), (II), (II-A), (III),(III-A) and (III-B), only T_(d1) and T_(d1)′ where n=3, 4, 5 arepreferably made to have values different from constant T_(d1) andT_(d1)′ at other n.

Specifically, when T_(d1)′ at n=3, 5 is represented by T_(d1a) andT_(d1c), respectively, T_(d1) at n=4 is represented by T_(d1b), andT_(d1) and T_(d1)′ at n being at least 6 are represented by T_(d1d), itis preferred that at least one of T_(d1a), T_(d1b) and T_(d1c) has avalue different from T_(d1d).

More preferably, when T_(d1) and T_(d1)′ where n is at least 6 are madeto have a constant value T_(d1d), T_(d1)′ at n=3, 5 is made to beT_(d1a) and T_(d1c), respectively, and T_(d1) at n=4 is made to haveT_(d1b), T_(d1a)<T_(d1b)≦T_(d1c)≦T_(d1d).

In the recording pulse division methods (II), (II-A), (III), (III-A) and(III-B), it is particularly effective to make T_(d1)′ and T_(d1) at n=3,4, 5 to be different from T_(d1) in the case where n is at least 6,whereby the recording power margin for space length jitter, particularly3T space length jitter, can be improved by the simplest pulse-generatingcircuit.

In some cases, while on the basis of the recording pulse division method(I), it is necessary to simplify it by reducing the number ofindependent parameters on one hand, it will be necessary to finelyadjust the recording pulse division method to form n₀T mark dependingupon the combination of the preceding and succeeding record marks n₁Tand n₂T, and further upon the combination of space length n_(1s)Tbetween n₁T mark and n₀T mark and space length n_(2s)T between n₀T markand n₂T mark, in recording specific n₀T mark, taking into considerationthe influence of the remaining heat due to heat diffusion from thepreceding and succeeding record marks.

Here, in CD, n₀, n₁, n₂, n_(1s) and n_(2s) are any one of integers 3 to11. Further, in DVD, n₀, n₁, n₂, n_(1s) and n_(2s) are any one ofintegers represented by n=3 to 11 and 14.

Also in this case, it is preferred to finely adjust especially (T_(d1),α₁, α_(m),β_(m)) among the above-mentioned parameters for defining therecording pulse division method to form n₀T mark depending upon thecombination of (n₁, n_(1s), n₀, n_(2s) and n₂). Further, in recording ofn₀T mark, reference may be made to some of (n₁, n_(1s), n₀, n₂s and n₂).

Further, the thermal interference becomes distinct in a case where spacelengths are short. Accordingly, only when n_(1s) and n_(2s) are 3,(T_(d1), α₁, α_(m) and β_(m)) may be different from a case where n_(1s)and n_(2s) take other values. It is especially effective and preferredto adjust (T_(d1) and β_(m)).

In the above-described recording method, good overwriting can be carriedout while ensuring interchangeability with the CD-RW standards. Namely,the signal characteristics after overwriting EFM modulation signals, canmaintain such a record quality that the above-mentioned modulation m₁₁is at least 60%; interchangeability with CD is secured in the vicinityof asymmetry being 0; further, jitters of the respective marks andbetween marks (spaces) of retrieving signals are at most 35 nsec (at thetime of retrieving at 1-time velocity); and the mark lengths and betweenmarks have lengths of substantially nT×V (where T is the reference clockperiod of data, n is an integer of from 3 to 11, and V is a linearvelocity at the time of retrieving). This means that retrieving canpractically be carried out at a low error rate by a commerciallyavailable CD-ROM drive capable of retrieving CD-RW disks.

Further, in the above-mentioned recording method, good overwriting canbe carried out while ensuring interchangeability with RW-DVD standards.Namely, the signal characteristics after overwriting EFM+ modulationsignal can maintain such a record quality that the above-mentionedmodulation m₁₄ is at least 55%; interchangeability with DVD can besecured in the vicinity of asymmetry being 0; and further jitter ofretrieved signals is at most 15% (at the time of retrieving at 1-timevelocity) or even at most 10%. This means that retrieving canpractically be carried out at a low error rate by a commerciallyavailable DVD-ROM drive capable of retrieving RW-DVD disks.

5. Regarding the Recording Method at a Plurality of and in a Wide Rangeof Linear Velocities

Now, the recording method according to the fourth aspect of the presentinvention will be described.

The medium of the present invention as a rewritable optical recordingmedium can be excellently retrieved by a conventional system capable ofretrieving CD-RW at least in case of an optional linear velocity from alower limit of 8 or 10-times velocity to an upper limit of a high linearvelocity of 24 or 32-times velocity, if its recording method is set.Simultaneously the compatibility of medium and drive can be carried outeasily.

And, if the above-mentioned divided recording pulse generation method(II) or (III) is employed, the optimum divided recording pulse strategycan easily be found by setting the switching period of recording pulsesto be constant generally at 2T and changing the duty ratio of α_(i) toβ_(i) (and α_(i)′ to β_(i)′) (where i=1 to m−1), even when the samemedium is used at different linear velocities.

In such a case, at any linear velocity, it is common to employ a pulsedivision method as shown in FIG. 5 wherein writing power Pw and biaspower Pb are alternatively applied to form a mark having length nT.However, the optimum values of parameters determining its specificsystem usually vary depending upon the linear velocity. Therefore, withthe medium of the present invention, it is preferred to preliminarilyrecord on the medium the optimum writing power Pw₀, the optimum erasingpower Pe₀ and the optimum bias power Pb₀ corresponding to the recordinglinear velocity, or at least one of pulse division information such asα_(i) (i is at least one of from 1 to m), β_(i) (i is at least one offrom 1 to m), the division number m, etc.

And, on the basis of the recording pulse division method (I), therecording pulse division method (IV) is applied.

Recording Pulse Division Method (IV)

This is an optical recording method employing the above-mentionedrecording pulse division method (I), wherein the rewritable opticalrecording medium is a circular disk, and recording is carried out at aplurality of recording linear velocities while controlling the recordinglinear density to be constant so that it will be the same as in a diskCLV-recorded at 1-time reference velocity, in the same disk plane, andα_(i)=α_(imax) (where i=1 to m) at the maximum linear velocity V_(max)is from 0.5 to 2, and α₁′=α_(imax) (where i=1 to m) at the V_(max) isfrom 0.5 to 2, and α_(i) and α_(i)′ (where i=1 to m) are permitted tosimply decrease as the linear velocity lowers.

A recording pulse division method may be defined in a similar manneralso for each of (II), (II-A), (III), (III-A) and (III-B) derived fromthe recording pulse division method (I). The following “Recording pulsedivision method (V)” is a case where the recording pulse division method(II) is employed in the recording pulse division method (IV).

Further, in the following description, with respect to the referencelinear velocity of 1-time velocity, the maximum linear velocity V_(max)and the minimum linear velocity V_(min) the respective values aredifferentiated between CD-RW and RW-DVD unless otherwise specified.

Namely, the reference linear velocity V₁ of 1-time velocity is from 1.2m/s to ¼ m/s in the case of CD-RW, and 3.49 m/s in the case of RW-DVD.

Further, the maximum linear velocity V_(max) is, in the case of CD-RW, alinear velocity within a range of from 20 to 32-times velocity of theabove-mentioned reference linear velocity of CD-RW, particularly 20, 24or 32-times velocity. In the case of RW-DVD, it is a linear velocity inthe range of from 4 to 12-times velocity of the above-mentionedreference linear velocity of RW-DVD, particularly 4, 5, 6, 8, 10 or12-times velocity.

Likewise, the minimum linear velocity V_(min) is, in the case of CD-RW,a linear velocity of at most about 22-times velocity, and in the case ofRW-DVD, a linear velocity of at most about 7-times velocity. As a matterof course, when V_(max) and V_(min) are used in a pair, they areselected from a linear velocity range where V_(max)>V_(min).

Accordingly, in the following description, when CD-RW is expected, theabove-described values for CD-RW will be used as the reference linearvelocity of 1-time velocity, V_(max) and V_(min), and when RW-DVD isexpected, the above-described values for RW-DVD will be employed as thereference linear velocity of 1-time velocity, V_(max) and V_(min).

Recording Pulse Division Method (V)

This is an optical recording method employing the above-mentionedrecording pulse division method (II), wherein the rewritable opticalrecording medium is a circular disk, and recording is carried out at aplurality of recording linear velocities while controlling the recordinglinear density to be constant so that it will be the same as in a diskCLV-recorded at 1-time reference velocity in the same disk plane,wherein α_(i)=α_(imax) (where i=1 to m) at the maximum linear velocityV_(max) is from 0.5 to 2, and α₁′=α_(imax)′ (where i=1 to m) at theV_(max) is from 0.5 to 2, and α_(i) and α_(i)′ (where i=1 to m) arepermitted to monotonically decrease as the linear velocity lowers.

Further, a case wherein the recording pulse division method (II-A) isemployed in the above recording pulse division method (V), will bedesignated as a recording pulse division method (V-A).

Further, a case wherein the recording pulse division method (III) isemployed in the recording pulse division method (IV), will be designatedas a recording pulse division method (VI) as follows.

Recording Pulse Division Method (VI)

This is an optical recording method employing the above-mentionedrecording pulse division method (III), wherein the rewritable opticalrecording medium is a circular disk, and recording is carried out at aplurality of recording linear velocities while controlling the recordinglinear density to be constant so that it will be the same as in a diskCLV-recorded at 1-time reference velocity in the same disk plane,wherein α_(i)=α_(imax) (where i=1 to m) at the maximum linear velocityV_(max) is from 0.5 to 2, and α₁′=α_(imax)′ (where i=1 to m) at theV_(max) is from 0.5 to 2, and α_(i) and α_(i)′ (where i=1 to m) arepermitted to monotonically decrease as the linear velocity lowers.

Here, a case wherein the recording pulse division method (III-A) isemployed in the above recording pulse division method (VI), will bedesignated as a recording pulse division method (VI-A). Further, arecording pulse division method wherein the recording pulse divisionmethod (III-B) is employed in the above recording pulse division method(VI) will be designated as a recording pulse division method (VI-B).

Further, in each of the above recording pulse division methods (IV), (V)and (VI), “permitted to monotonically decrease” means that when α_(i) atthe minimum linear velocity V_(min) to carry out overwriting isrepresented by α_(imin) (i=1 to m), α_(imin)<α_(imax) is satisfied withrespect to all n and i. However, at an intermediate linear velocitybetween V_(min) and V_(max), α_(i) may sometimes be constantirrespective of the linear velocity, but, as a standard rule, it takes asmaller value at a lower linear velocity.

Further, the comparison of “large” or “small” of α_(i) is carried outwith respect to individual α_(i) where i=1 to m for the same n.

At V_(max), α_(imax) and α_(imax)′ are set to be about 1, morespecifically from 0.8 to 1.5. Especially with respect to i=2 to m−1,α_(imax) and α_(imax)′ are preferably within a range of from 0.8 to 1.2.Namely, at V_(max), Σ_(i)(α_(imax)) and Σ_(i)(α_(imax)′) are desired tobe about n/2 or a value smaller than n/2.

And, α_(imin) is desired to take a value smaller than α_(imax) within arange of η₀(V_(min)/V_(max))α_(imax), where η₀=0.8 to 1.5, and at anintermediate linear velocity between V_(min) and V_(max), α_(i) takes avalue between such α_(imin) and α_(imax). More preferably, η₀ is withina range of from 1 to 1.3.

The same applies to α₁′, α_(imin)′ and α_(imax)′ (i=1 to m).Accordingly, Σ_(i)(α_(i)) and Σ_(i)(α_(i)′) will monotonically decreaseas the linear velocity lowers.

Further, also when n=3, α₁′ is set to monotonically decrease as thelinear velocity lowers. On the other hand, T_(d1)′ and β₁′ are permittedto monotonically increase as the linear velocity lowers.

Here, “controlling the recording linear density to be constant” meansthat VT is constant, where V is the recording linear velocity, and T isthe reference clock period at that time. Further, “controlling therecording linear density to be constant” means to set VT=V₁T₁ where T₁is the reference clock period at the reference linear velocity V₁ i.e.1-time velocity. Thus, retrieving by the same retrieving system as forCD will be possible in a case where retrieving is carried out at aconstant linear velocity irrespective of the degree of the linearvelocity at the time of recording. Here, VT is permitted to have adeviation from V₁T₁ to such an extent as allowable from the nature ofthe retrieving circuit for CD, i.e. usually a deviation at a level of±5%.

Further, for CD-RW, it is preferred to set 1-time velocity to be 1.2m/s, whereby the physical length of a mark can be made small, and therecording linear density can be increased. In such a case, a capacity offrom 650 to 700 MB can be accomplished.

To simplify the pulse-generating circuit, it is preferred that at eachm, T_(d1)+α₁, β_(i−1)+α₁, T_(d1)′+α₁′, and β_(i−1)′+α_(i)′ (i=1 to m, atleast i=3 to m−2) are substantially constant irrespective of the linearvelocity. Especially for a mark of m being at least 3, they arepreferably constant except for inevitable fluctuation by the nature ofthe electronic circuit.

Specifically, within a linear velocity range of from V_(min) to V_(max),it is preferred that when m is at least 3, T_(d1)+α₁, T_(d1)′+α₁′,β_(i−1)+α₁=2, and β_(i−1)′+α_(i)′=2 (i=3 to m−1) are, respectively,constant irrespective of the linear velocity.

Especially when the recording pulse division method (VI-B) correspondingto the recording pulse division method (III-B) is employed, it isparticularly preferred to set T_(d1)+α₁=T_(d1)′+α₁′=2 at any linearvelocity and to set β_(i−1)+α_(i) where i=2 to m to be constant at 2 andto set β_(i−1)′+α_(i)′ where i=2 to m−1 to be constant at 2 and to setβ_(i−1)′α_(i)′+α_(i)′ where i=2 to m−1 to be constant at 2. By such asetting, it will be possible to synchronize β_(i−1)+α_(i)(β_(i−1)′+α_(i)′) where i=2 to m−1 with 2T period. This means that inFIG. 5, the system can be constituted solely by a circuit having gatesG1 and G2 synchronized with period 2T. And, even if T is made to bevariable depending upon the linear velocity, it is possible to obtain arecording pulse strategy capable of accommodating any linear velocitysimply by changing only the duty ratio of α_(i) at G1 and G2, whereby itwill be possible to simplify the design of the control circuit(electronic circuit) to generate laser beams (pulsed beams) forrecording pulses and off-pulses of the recording pulse strategy.

On the other hand, β_(m) and β_(m)′ are usually within a range of from 0to 2 and permitted to monotonically increase as the linear velocitylowers. The meaning of “monotonically increase” is the same as in thecase of “monotonically decrease” with respect to the above-mentionedα_(i) and α_(i)′, and at an intermediate linear velocity between V_(min)and V_(max), β_(m) and β_(m)′ may sometimes be constant irrespective ofthe linear velocity, but as a standard rule, it should take a largervalue at a lower linear velocity.

Like β_(m), β_(m)′ may be within a range of from 0 to 2. However, in thecase of n=3 at a low linear velocity of at most about 16-times velocityin the case of CD-RW, β_(m) and β_(m)′ are preferably made to have avalue within a range of from 0 to 3.

Accordingly, by setting β_(m)=0 to 2 and β_(m)′=0 to 3 at any linearvelocity to be used and to let β_(m) and β_(m)′ monotonically increaseas the linear velocity lowers, it will be possible to carry out goodrecording at any linear velocity. Here, to let β_(m)′ monotonicallyincrease as the linear velocity lowers, means to let Δ_(m)′monotonically increase as the linear velocity lowers.

In fact, in the recording pulse division method (VI-B), it is preferredthat β_(m) is permitted to monotonically increase as the linear velocitylowers, and also Δ_(m)′ is permitted to monotonically increase.

Further, in the recording pulse division method (VI-A) or (VI-B), it ispossible to further reduce the number of parameters by setting eitherΔ_(m−1) or Δ_(m)′ to be 0 or setting Δ_(m−1)=Δ_(m). It is a feature ofthe recording medium of the present invention that even if the number ofparameters is reduced in this manner, good characteristics can beobtained. And, among recording media of the present invention, thetendency to obtain the above-mentioned good characteristics will beparticularly distinct with an optical recording medium employing a GeSbtype recording layer. Namely, by using an optical recording mediumemploying a GeSb type recording layer, the effect of the presentinvention such that good high velocity recording characteristics can berealized by a simple recording pulse division method, will be mosteffectively be provided.

Further, to obtain accurate 3T mark lengths and low jitter at eachlinear velocity, it is preferred that among T_(d1)′, α₁′ and β₁′ wheren=3, T_(d1)′ and β₁′ are permitted to monotonically increase as thelinear velocity lowers, and all is permitted to monotonically decreaseas the linear velocity lowers.

Thus, by a simple combination of logic gates as shown in FIG. 5,recording pulses can easily be generated by changing the data referenceclock period T at each linear velocity.

Here, it is further preferred for simplification that within a linearvelocity range of from V_(min) to V_(max), T_(d1)+α₁, T_(d1)′+α₁′,β_(i−1)+α_(i)=2 and β_(i−1)′+α_(i)′=2 (i=3 to m−1) are, respectively,constant irrespective of the linear velocity where m is at least 3.

Further, it is more preferred that when m is at least 2, these valuesare constant irrespective of the linear velocity.

With respect to other periods, in the case of CD-RW, at least in alinear velocity range of about 2-time velocity, the linear velocitydependency of the respective parameters in the recording pulse divisionmethod is relatively small, whereby it is preferred that some or all ofthe values of β_(m−1)+α_(m) and β₁+α₂ in an even number length mark withm being at least 2, and β_(m−1)′+α_(m)′ and β₁′+α₂′ in an odd numberlength mark with m being at least 2, are made to be substantiallyconstant irrespective of the linear velocity.

Here, the linear velocity range of about 2-times velocity in the case ofCD-RW means that in a case where V_(min)=8-times velocity andV_(max)=24-times velocity, these parameters may be changed generallyevery 2-times velocity, like for a range of from 8 to 10, from 10 to 12,from 12 to 14, from 14 to 16, from 16 to 18, from 18 to 20, from 20 to22, or 22 to 24-times velocity.

On the other hand, in the case of RW-DVD, at least in a linear velocityrange of about 0.5-time velocity, the linear velocity dependency of therespective parameters of the recording pulse division method isrelatively small, whereby it is preferred that some or all of the valuesof β_(m−1)+α_(m) and β₁+α₂ in an even number length mark with m being atleast 2 and β_(m−1)′+α_(m)′ and β₁′+α₂′ in an odd number length markwith m being at least 2, are made to be substantially constantirrespective of the linear velocity.

Here, the linear velocity range of about 0.5-time velocity in the caseof RW-DVD means that for example, in a case where V_(min)=2-timesvelocity and V_(max)=6-times velocity, these parameters may be changedgenerally every 0.5-time velocity like for a range of from 2 to 2.5,from 2.5 to 3, from 3 to 3.5, from 3.5 to 4, from 4 to 4.5, from 4.5 to5, from 5 to 5.5 or from 5.5 to 6-times velocity.

Of course, it is more preferred that these values are constant at everylinear velocity within a range of from V_(min) to V_(max). In therecording pulse division method (VI), (VI-A) or (VI-B), even if β₁+α₂and β_(m−1)+α_(m) in an odd number length mark of m being at least 3 aremade to be constant at any linear velocity within a range of fromV_(min) to V_(max), good recording signal quality can relatively easilybe obtained, and it is particularly suitably applied. In such a case, itis more preferred that they are made to be constant at β₁+α₂=2 andβ_(m−1)+α_(m)=2.

The “period is constant” means that it is constant within a range wherethe resolution of the value set by the division pulse-generating circuitallows, and when it is standardized by the clock period T, fluctuationless than ±0.01T is allowable.

Referring again to FIG. 4, the significance of the recording pulsedivision methods (IV), (V) and (VI) will be explained taking CD-RW as anexample. If α_(i) and β_(i) used satisfactorily at 24 or 32-timesvelocity for the recording medium of the present invention, are used asthey are in the entire linear velocity range of from 8 to 32-timesvelocity, and low velocity recording is carried out simply by settingthe reference clock period for data to be variable, the cooling rate ofthe recording layer at the low linear velocity will remarkably decrease,like curve e shown by a dotted line in FIG. 4, whereby formation of anamorphous phase will be hindered. At a low linear velocity, thereference clock period T becomes relatively large as compared with thecase of a high linear velocity, whereby the absolute time forirradiation of off-pulses will be long, but at the same time, theabsolute time for irradiation of recording pulses will also be long, andconsequently, the irradiation energy per unit time will also increase,whereby the cooling rate will decrease. Accordingly, in the 2T baserecording strategy in the present invention, the recording pulse dutyratio is lowered to prolong the off-pulse sections as the linearvelocity lowers, whereby the decrease in the cooling rate at a lowlinear velocity is complemented to realize the characteristicscorresponding to curve d in FIG. 4.

“Recording method CD2-3” and “Recording method DVD2-3” are capable ofsimply prescribing a recording medium having characteristics withinspecific ranges, particularly by defining the ranges of variousparameters in the recording pulse division method (VI-B) and combiningthem with “Recording method CD1-3” or “Recording method DVD1-3” tounivocally define curve d in a very limited range in FIG. 4.

Further, it is preferred to set β_(i)T (i=1 to m) and β₁′T (i=1 to m−1)to be at least 2 nsec at any linear velocity to be used. Specifically,if α_(i)T and α_(i)′T (i=1 to m) and β_(i)T and β_(i)′T (i=1 to m−1) areset to be at least 2 nsec at any radial position of the opticalrecording medium, it will be possible to properly carry out recordingalso by the after-mentioned CAV recording or P-CAV recording.

In the above-mentioned methods, Pb, Pw and the Pe/Pw ratio arepreferably set to be constant irrespective of the linear velocity duringoverwriting. When the optimum writing power is represented by Pw₀ andthe optimum erasing power is represented by Pe₀ at a linear velocity Vwithin a range of from V_(min) to V_(max), Pw₀ and Pe₀ are usuallyselected so that the jitter or the error rate will be lower thanspecific levels. Pe₀ is usually selected so that the Pe₀/Pw₀ ratiobecomes constant, and the ratio is usually from 0.2 to 0.6, preferablyfrom 0.2 to 0.4, more preferably from 0.3 to 0.4. Further, if Pw₀ ishigh, deterioration by repeated overwriting will be accelerated, and theprescribed number of repeated overwriting is usually preferably set tobe at least 1000 times. Pw₀ determined from such viewpoints may be onewhich varies depending upon the linear velocity, but the ratio of theminimum value to the maximum value of Pw₀ within the above linearvelocity range is desired to be at least 0.8.

In such a case, it is preferred that information relating to the writingpower, etc. and pulse division information are preliminarily written onthe desk as concavo-convex pit signals or groove-deformation signals. Asa result, the optimum pulse strategy can be automatically selected by adrive for recording. The information to be preliminarily writtenincludes, for example, at least the values of the minimum and maximumlinear velocities V_(min) and V_(max) for overwriting, themselves, theoptimum Pe/Pw ratios at V_(min), V_(max) and several linear velocity Vbetween them, the optimum writing power Pw₀, the optimum erasing powerPe₀, the optimum bias power Pb₀ and the numerical values of all or someof independent parameters as described for the recording pulse divisionmethods (II-A), (III-A) and (III-B). However, it is preferred that Pb₀is usually constant and is the same as the retrieving power Pr.

As the above linear velocity V, in the case of CD-RW, it may be selectedwith intervals generally larger than about 4-times velocity, and forexample, in 8 to 24-times velocity, it may be selected like 8, 12, 16,20 and 24-times velocities, but may be smaller than this.

As the above linear velocity V, in the case of RW-DVD, it may beselected with intervals generally larger than about 1-time velocity, andfor example, in 2 to 6-times velocity, it may be selected like 2, 3, 4,5 and 6-times velocities, but may be smaller than this.

Particularly, in (VI-B) corresponding to the recording pulse divisionmethod (III-B), if a total of eleven parameters, i.e. αc, Δ_(m−1),Δ_(m), β_(m) and Δ_(m)′ where n is at least 4, T_(d1)′, α₁′ and β₁′where n=3 and Pw, Pe and Pb, are defined, the recording pulse divisionmethod to form all mark lengths of from 3 to 11 will be fixed. It ispreferred that these eleven independent parameters are optimized forpreliminarily selected every linear velocity and preliminarily writtenon the disk.

Also in a case where recording is carried out at a linear velocity notpreliminarily selected in the after-mentioned CAV or P-CAV recording,some or all values of the above parameters at preliminarily selectedrecording linear velocity may be read out, and by means of such values,it will be possible to calculate the optimum parameters (such as αc,etc.) of the recording pulse strategy in recording at theabove-mentioned linear velocity not preliminarily selected. Accordingly,if the above eleven independent parameters are optimized for everypreliminarily selected linear velocity and written on the disk, goodoverwriting will be possible at an optional linear velocity betweenV_(min) and V_(max).

Thus, by combining the recording medium of the present invention withthe recording method of the present invention which makes one beamoverwriting possible at a plurality of linear velocities, the followingtwo practical usages will be possible.

Practical Usage 1

Firstly, with a current CD device, the rotational speed by a spindlemotor to rotate a disk is limited to a level of 10000 rpm at themaximum. A polycarbonate resin having molecular weight of from 12000 to20000 which is commonly used as a substrate for CD, is likely to bebroken by a centrifugal force at a rotational speed higher than this.CD-RW usually has a disk shape having a diameter of 12 cm and has arecord area (information area) having a radius of at least 23 mm to 58mm, preferably from 22 to 58 mm. If the disk is rotated at about 8000rpm, the linear velocity at the innermost periphery of the record areawill be 16-times velocity, and the linear velocity at the outermostperiphery of 58 mm will be about 38-times velocity. At 10000 rpm, thelinear velocity at the innermost periphery of record area will be about22-times velocity, and the linear velocity at the outermost peripherywill be about 48-times velocity, whereby recording by a CLV system for aconstant linear velocity at least about 22-times velocity over theentire surface, is impossible.

In the case of a DVD device, when rotated at about 10000 rpm, about7-times velocity at the inner periphery and about 16-times velocity atthe outer periphery are almost limits from the relation of the strengthof the substrate like in the case of CD. However, in the case of RW-DVDof the present invention, the upper limit in the recording velocity isfrom about 10 to 12-times velocity, whereby from about 6000 to 7000 rpmwill be the upper limit of the rotational speed for overwriting.

Accordingly, in practical usage 1, a recording system to increase thelinear velocity gradually from the inner peripheral portion is adoptedin a CD-RW recording or retrieving device to carry out recording orretrieving at a linear velocity of at least 24-times velocity at themaximum at the outermost peripheral portion of the record area or in aRW-DVD recording or retrieving device to carry out recording orretrieving at a linear velocity of at least 7-times velocity at themaximum at the outermost peripheral portion of the record area. This isreferred to as P-CAV (partial CAV) or ZCLV (zoned CLV).

Here, in the case of CD-RW, P-CAV is such that by setting the velocityat the innermost periphery of the record area at from 16 to 22-timesvelocity, recording is carried out by a CAV system up to a radius Rswhere the velocity will be from 24 to 32-times velocity, and at a radiusoutside of Rs, CLV recording is carried out at a constant linearvelocity of from 24-times velocity to 32-times velocity.

On the other hand, ZCLV is such that up to the radius of Rs, a CLVrecording is carried out at a relatively low linear velocity such as16-times velocity or 20-times velocity while switching the linearvelocity for every zone, whereby the linear velocity is increasedtowards the outer periphery.

On the other hand, in the case of RW-DVD, P-CAV is such that by settingthe velocity at the innermost periphery of the record area at from 4 to7-times velocity, recording is carried out by a CAV system up to aradius Rs where the velocity will be from 8 to 10-times velocity, and ata radius outside of Rs, CLV recording is carried out at a constantlinear velocity of from 8-times velocity to 10-times velocity.

On the other hand, ZCLV is such that up to the radius Rs, CLV recordingis carried out at a relatively low linear velocity such as 4-timesvelocity or 6-times velocity while switching the lineal velocity forevery zone, whereby the linear velocity as increased towards the outerperiphery.

Practical Usage 2

This is a practical usage whereby CD-RW or RW-DVD of which recordingused to be carried out only by a CLV mode, will be made recordable by acomplete CAV mode, and is a practical method whereby a poor access orseek performance which used to be a weak point of a CD-RW medium whichalways required rotational synchronization, can be improved to a largeextent. This is particularly efficient to carry out access to packets atskipping radial positions in random packet recording, wherebyconvenience as a medium for an external memory device of a computer willbe substantially increased. Further, CLV consumes a large amount ofelectric power for acceleration or deceleration of a motor to change therotational speed. Whereas, there is no such a necessity, and there is amerit that the power consumption of the drive can be improved to a largeextent.

In the present invention, in accordance with at least either one of therecording pulse division methods (IV) to (VI), α_(i) and α_(i)′ (i=1 tom) are permitted to simply decrease, while β_(m) and β_(m)′ arepermitted to simply increase, as the linear velocity lowers. Usually,the recording pulse division method itself is set to be constant, whilethe respective parameters (Pw, Pe, Pb, T_(d1), α_(i), β_(i), etc.) ineach division method are made variable.

And, in the case of CD-RW, irrespective of which one of the aboverecording pulse division methods (IV) to (VI) is used, when EFMmodulation information is recorded on a disk-shaped rewritable opticalrecording medium by a plurality of mark lengths, a linear velocity offrom 1.2 m/s to 1.4 m/s is used as the reference velocity (1-timevelocity), and it is preferred to rotate the optical recording medium sothat the linear velocity at the outermost periphery of the record areaof the optical recording medium will be at least 20-times velocity.

Especially when P-CAV (partial CAV) or ZCLV (zoned CLV) is employed as arecording system to gradually increase the linear velocity from theinner peripheral portion, it is preferred to rotate the disk so that thelinear velocity at the innermost periphery of the record area will be atleast 16-times velocity of the reference linear velocity, and therecording linear velocity will be high towards the outer periphery.

On the other hand, in the case of RW-DVD, irrespective of which one ofthe above recording pulse division methods (IV) to (VI) is used, whenEFM+ modulation information is recorded on a disk-shaped rewritableoptical recording medium by a plurality of mark lengths, a linearvelocity of 3.49 m/s is used as the reference velocity (1-timevelocity), and it is preferred to rotate the optical recording medium sothat the linear velocity at the outermost periphery of the record areaof the optical recording medium will be at least 5-times velocity.

Particularly, when P-CAV (partial CAV) or ZCLV (zoned CLV) is used as arecording system to gradually increase the linear velocity from theinner peripheral portion, it is preferred to rotate the disk so that thelinear velocity at the innermost periphery of the record area will be atleast 4-times velocity of the reference linear velocity, and therecording linear velocity becomes higher towards the outer periphery.

In the case of CD-RW and RW-DVD, when a complete CAV mode or a P-CAVmode is used for recording or a ZCLV mode is used for recording, underthe above conditions, it is preferred that the record region is dividedinto a plurality of virtual zones in every certain radius, and β_(m)=0to 3, and further, β_(m) is made to monotonically increase towards theinner peripheral zone, and α_(i) and α_(i)′ are made to monotonicallydecrease towards the inner peripheral zone.

Further, with a view to simplifying the recording device, it ispreferred that the values of Pb, Pw and Pe/Pw are substantially constantat any radial position of the optical recording medium.

In the ZCLV system (Practical method 1), the reference clock period Tand parameters of the recording pulse division method are switched forevery CLV zone. On the other hand, in a CAV zone of the CAV system(Practical usage 2) or P-CAV method (Practical usage 1), the linearspeed continuously changes depending upon the radial position, and thereference clock period is also made to continuously change. On the otherhand, for the parameters of the recording pulse division method, it ispreferred that a virtual zone is set generally for every predeterminedlinear speed, thus for every predetermined radial width, and theparameters are made to be constant within each zone and to be switchedfor every zone. The width of such a virtual zone is preferably to be arange wherein the linear velocity changes from about 0.5-time velocityto 2-times velocity. Further, the width of every zone is preferably madeto be basically constant, but it is also preferred that as the linearspeed increases, i.e. towards the outer periphery, the width of the zoneis gradually reduced. As the linear speed increases, a value such asjitter is likely to deteriorate, and it is necessary to frequentlychange to the optimum parameter.

Heretofore, in the retrieving system for CD-ROM and DVD-ROM, retrievingin a CAV mode has already been carried out, but at the time ofrecording, CAV was possible only at a speed of from 4 to 10-timesvelocity for CD-ROM and only at a speed of from 1 to 2.5-times velocityfor RW-DVD, and therefore, it has been in practice to carry outretrieving by increasing the rotational speed at the time of retrieving.If the maximum overwriting linear velocity is at this level, recordingcan be made in a shorter period by carrying out the recording only byCLV, and accordingly, there has been little merit in recording by a CAVmode. However, like in the present invention, if the maximum overwritinglinear speed can be made to be at least 24-times velocity for CD and atleast 6-times velocity for DVD, merits to shorten the access time or toreduce the power consumption, by the complete CAV recording, can easilybe obtained.

As mentioned above, CD-RW is usually of a disk-shape having a diameterof 12 cm and has a record area (information area) having a radius of atleast 23 mm to 58 mm, preferably from 22 to 58 mm. If this disk isrotated at about 5000 rpm so that the velocity will be 10-times velocityat the inner periphery of the record area, the linear velocity at theoutermost periphery of 58 mm of the record region will be about 24-timesvelocity. Namely, usually, if the innermost periphery is made to be10-times velocity by a CAV system, the outermost periphery becomes about24-times velocity. Likewise, if the linear velocity at the outermostperiphery of the record area is made to be 32-times velocity, the linearvelocity at the innermost periphery of the record area will be about13-times velocity.

Further, RW-DVD is usually of a disk shape having a diameter of 12 cmand has a record area (information area) having a radius of at least 23mm to 58 mm, preferably from 22 to 58 mm. If this disk is rotated atabout 5000 rpm so that the velocity will be 2.5-times velocity at theinnermost periphery of the record area, the linear velocity at theoutermost periphery of 58 mm of the record area will be about 6-timesvelocity. Namely, usually, if the innermost periphery is made to be2.5-times velocity by a CAV system, the outermost periphery will beabout 6-times velocity. Likewise, if the linear velocity at theoutermost periphery of the record area is made to be 10-times velocity,the linear velocity at the innermost periphery of the record area willbe about 4-times velocity.

At that time, if the reference clock period T is changed in inverseproportion to the radial distance so that the product VT with the linearvelocity V at any radial position, will be constant, the mark length nTwill be constant irrespective of the rotation angular velocity, wherebyrecording with a constant linear density which is interchangeable withCD for retrieving only or with DVD for retrieving only, will bepossible, while it is recording in a complete CAV mode.

Here, the record area includes, in addition to the record area foruser's data, an area for trial writing, lead-in and lead-out areas, etc.to be used by the system. Accordingly, the radial positions of 22 mm and58 mm may contain an error at a level of ±1 mm. Further, incorrespondence with this allowable error, a certain deviation willresult also in the frequency value, etc., but such a deviation is alsoallowable.

A schematic view of the construction of a recording device to realizethe recording method of the present invention is shown in FIG. 6 takingCD-RW as an example.

In FIG. 6, the optical disk D1 has a substrate having a helical groovewobbled in accordance with signals modified by address information andhaving a carrier frequency f_(L0) having a constant spatial frequency(f_(L0) represents a carrier frequency during CLV recording), and arecording layer, and it has address information to distinguish a recordblock being a record information unit located at a predeterminedposition in the helical groove, and a synchronization signal todistinguish the start position of such a block. In FIG. 6, particularlyspecifically, a rewritable compact disk is supposed as the optical disk,whereby f_(L0)=22.05 kHz, and the address information is ATIPinformation frequency-modulated by ±1 kHz, using f_(L0) as the carrierfrequency. Further, the wobble is formed by groove wobbling so that whenretrieving is carried out at a linear velocity of from 1.2 m/s to 1.4m/s, the carrier frequency f_(L0) will be 22.05 kHz.

The optical disk recording/retrieving device 1 has a spindle motor M1 asa means to rotate the disk at an equal angular velocity about the centerportion of the disk as an axis, and a linear motor as a moving mechanism(LM1) to move in a radial direction an optical pickup to generate afocused laser beam for recording/retrieving, to a predetermined address.The pickup PU1 contains a focusing servo circuit (FE1) to adjust thefocal point of the focused laser beam generated from a laser diode asthe light source, to the recording layer surface of the optical disk,and a groove-tracking servo circuit (TE1) to let the focused laser beamscan along the helical groove. For the focusing servo circuit, a knownmethod such as an astigmatic method may be employed. For the trackingservo circuit, a known method such as a push-pull method or 3-beammethod may be employed (see “Compact Disk Book” third edition, Ohmsha,coauthored by Hetaro Nakajima and Hiroshi Ogawa).

The optical disk recording/retrieving device 1 further has a circuit(WAD1) to detect and decode the carrier frequency f_(A0) from the groovewobble, the address information and the block synchronizing signal, acircuit to generate a record data train, mark length-modified byencoders ED1 and ED2 in synchronization with the start position of therecord block and with the reference clock T (frequency f_(d0)) of data,and a circuit (WP1) to modulate the laser writing power incorrespondence with the record data train.

The optical disk D1 is CAV-driven by the motor M1. The disk isCAV-rotated at a rotational speed ω₀ between from 5000 to 7000 rpm, sothat the linear velocity will be 10-times velocity or 13-times velocityof 1.2 m/s to ¼ m/s, particularly at the innermost periphery of therecord area with a radius of about 22 mm. CAV-rotation is maintainedwith precision such that the rotational jitter is not more than a few %by monitoring the rotation of the spindle motor M1 by a tachometer andfeeding back the error from the prescribed rotational speed.

Decoding of the synchronization signal and the address information iscarried out by retrieving a push-pull signal P1 through anamplifier/filter system AF1, detecting the wobble signal, decoding theATIP signal, followed by decoding the contained synchronization signaland the address information. The address information and thesynchronization signal are referred to by an access/servo-controllingCPU1, and the predetermined address movement is controlled by CPU1. Theaddress movement comprises a radial movement by a coarse adjustmentmechanism by linear motor LM1 driving in a state where the trackingservo TE1 is switched off, and fine adjustment (fine adjustment of theinclination of the object lens of PU1) while referring to the ATIPaddress, with the tracking servo switched on, in the vicinity of thepredetermined address, but each one is controlled by CPU1.

Once it has been confirmed that a predetermined address has beenreached, the clock of the circuit CK1 as the data reference clockgenerator, is synchronized with the synchronization signal of ATIP, tocarry out recording at the predetermined ATIP frame. In the case ofCD-ROM data, encoding of ROM data is carried out by ED1, and thenencoding as CD is carried out by ED2. The data bit train is alsosynchronized with the reference clock of data, and the data train isfurther converted to a recording pulse train at WP1, to drive a laserdriver LD1 to carry out overwriting.

Further, retrieving is carried out in such a manner that after apredetermined address has been reached, the retrieving signal isretrieved through a RF signal-binarizing circuit system RF1, and whilesynchronizing the reference clock of data with the EFM frame, datadecoding as CD is carried out by ED2, and further, data decoding asCD-ROM is carried out by ED1.

In the recording method of the present invention, various methods areconceivable to generate the reference clock period T and a referenceclock of data in inverse proportion to the radial distance. However, thefollowing is conceivable as a preferred example. Here, description willbe made by taking as an example a case wherein a wobble carrierfrequency f_(L0) at 1-time velocity in a CLV mode is 22.05 kHz, thelinear velocities at the innermost periphery and the outermost peripheryof the record area in a CAV mode are 10-times velocity and 24-timesvelocity, respectively, and the reference clock of data is 196 times thecarrier frequency. Here, the carrier frequency f_(L0) allows an error ata level of ±0.1 from 22.05 kHz.

The medium has a helical groove having imparted a wobble having acarrier frequency of frequency f_(L0)=22.05 kHz as calculated at 1-timevelocity. This medium can be used as a usual CD-RW medium for a highvelocity recording in a CLV mode.

In a case where the wobble of a wobble groove (wobbling groove) isconstant at a frequency corresponding to the carrier frequencyf_(L0)=22.05 kHz, during CAV rotation, retrieved carrier frequencyf_(A0) of the wobble will change on appearance depending upon the radialposition i.e. depending upon the linear velocity corresponding to theradial position. And, a reference data clock frequency in proportion tothe radius can be obtained by multiplying by 196 the carrier frequencyf_(A0) of the wobble retrieved at the radial position during the CAVrotation. Here, f_(A0) represents the carrier frequency during the CAVrecording.

If recording is carried out in synchronization with this data referenceclock frequency in proportion to the radius, it is possible to carry outmark length modulation recording with a constant linear density even ina CAV mode.

Namely, if a wobble signal is written on the substrate in 1-timevelocity mode of CLV rotation, when the medium is CAV-rotated, it ispossible to make the spatial frequency to be constant i.e. to make thelinear density to be constant, by generating the reference clockfrequency of data by means of the same multiplying factor irrespectiveof the radial position.

For example, when the linear velocity at the innermost periphery of therecord area is 10-times velocity, and the linear velocity at theoutermost periphery of the record area is 24-times velocity, the carrierfrequency f_(A0) of a wobble retrieved in a CAV mode will be22.05×10=220.5 at the innermost periphery of the record area and22.05×24=529.2 kHz at the outermost periphery of the record area,respectively. The frequencies having them multiplied by 196 times, i.e.43.2 MHz (at the innermost periphery of the record area) and 103.72 MHz(at the outermost periphery of the record area) will be the referenceclock frequencies of data. In such a case, the reference clock period Tof data will be about 23.1 nsec at the innermost periphery of the recordarea and about 9.1 nsec at the outermost periphery of the record area.At an intermediate radial position, a reference clock period of data ininverse proportion to the radius between them, may be generated.

On the other hand, the wobble signal is usually frequency-modulated by±1 kHz with ATIP signal, and accordingly, the actual frequency is 22.05kHz±1 kHz and one period of the wobble signal will be accompanied by cfluctuation of about ±4.5%. If such a fluctuated signal is directlymultiplied by prescribed times to obtain a reference clock period ofdata, fluctuation (deviation) of the mark length of ±4.5% will resultagain. Usually, such fluctuation in the mark length recording is calleda phase shift, and if this shift is close to 5%, proper demodulation maynot be possible. Accordingly, in such a case, it is necessary to extractonly the carrier frequency f_(A0) from the frequency-modulated wobblesignal, followed by the predetermined multiplication.

Recently, there is a case to set the reference linear velocity to beslightly smaller than 1.2 m/s to a level of 1 m/s, the spatial frequencyof the wobble is made small, and the mark length is made shorter, forhigher density. Even in such a case, application of the recording mediumand the recording method of the present invention will not be hindered.

In the case of DVD, there are some differences such that the carrierfrequency f_(L0) in 1-time velocity retrieving is 144 kHz ( 1/157 ofclock frequency) in so-called DVD-RW standards or about 700 kHz ( 1/32of clock frequency) in DVD+RW standards, but basically, the device isconstituted on the totally similar principle.

6. Other Matters Relating to the Recording Method of the PresentInvention

Application of the Recording Method of the Present Invention to aConventional Low Linear Velocity Recording Medium

When overwriting is carried out on conventional 4 or 10-times velocityCD-RW or on 2 or 2.4 (2.5) or 4-times velocity RW-DVD by a recordingdevice whereby the recording method of the present invention can beapplied to CD-RW of at least 24-times velocity or RW-DVD of at least4-times velocity, as in the present invention, the conventional 1T basestrategy may be applied as it is, but it is possible to apply the 2Tbase recording pulse division method of the present invention. Namely,it is possible to carry out CLV recording at various linear velocitiesby applying the recording methods (I), (II), and (III) of the presentinvention, or to carry out CAV recording at 4 to 10-times velocity of10-times velocity CD-RW, or CAV recording at 1.6 to 4-times velocity of4-times velocity RW-DVD, by applying (IV), (V) and (VI).

Thus, the same recording pulse-generating circuit can be applied forrecording conventional CD-RW and RW-DVD, and CD-RW and RW-DVD of thepresent invention, whereby simplification of the pulse-generatingcircuit will be possible. On the other hand, in the conventional 1T baserecording pulse division method, it is practically impossible to carryout recording on a ultrahigh velocity medium as in the presentinvention.

For Rewritable Media of Other Formats

The recording medium of the present invention is not limited to anapplication to media having a specific format like CD-RW or RW-DVD. Forexample, it is applicable to a high density rewritable phase-changemedium employing blue LD (laser disk). Further, the mark lengthmodulation system is not limited to EFM or EFM+, and is applicable to,for example, so-called (1,7) run-length limited (RLL) non-return-to-zeroinverted (NRZI) modulation system where n=2, 3, 4, 5, 6, 7 or 8.

EXAMPLES

CD-RW Basic Example

A polycarbonate resin substrate having a thickness of 1.2 mm andprovided with a helical groove having a track pitch of 1.6 μm andwobbling in a reference frequency of 22.05 kHz as calculated at 1-timevelocity (1.2 m/s), was formed by injection molding.

The groove width was 0.54 μm and the depth was 34 nm. Each of thesevalues was obtained by an optical diffraction method of U grooveapproximation using a He—Ne laser beam having a wavelength of 633 mm. Tothe groove wobble, address information by ATIP was further imparted byfrequency modulation of ±1 kHz.

Then, on the substrate, a lower protective layer, a recording layer, anupper protective layer, a reflective layer and an ultraviolet-curableresin layer were formed in this order. Deposition of the respectivelayers was carried out by sequential lamination by sputtering on thesubstrate without releasing the vacuum. However, the ultraviolet-curableresin layer (thickness of about 4 μm) was coated by spin coating.

Immediately after the deposition, the recording layer was amorphous, andby irradiating a laser beam having a wavelength of from 810 to 830 nmand focused into an oval shape having a major axis of about 150 μm and aminor axis of about 1.0 μm, by selecting the linear velocity and theinitialization power within proper ranges, the entire surface wascrystallized to obtain an initial (unrecorded) state.

With respect to the thickness of each layer, the deposition rate wasaccurately measured, and then the thickness was controlled by thesputtering time. The composition of the recording layer was determinedby correcting the fluorescent intensities of the respective elementsobtained by a fluorescent X-ray analysis by the absolute compositionseparately obtained by a chemical analysis (atomic absorptionspectrometry).

The density of the recording layer or the protective layer was obtainedfrom the weight change when deposited on the substrate as thick as a fewhundred nm. The film thickness was determined by correcting thefluorescent X-ray intensity by the film thickness measured by a stylusmeter.

The sheet resistivity of the reflective layer was measured by a 4-probeohm meter (Loresta MP, tradename, manufactured by Mitsubishi Yuka(presently Dia Instruments)).

The measurement of the resistivity was carried out either by measuringthe reflective layer formed on a glass or polycarbonate resin substrateas an insulating substance, or by measuring the reflective layerconstituting the outermost layer after forming the above-mentioned fourlayers (lower protective layer/recording layer/upper protectivelayer/reflective layer). The upper protective layer is a dielectric thinfilm which is an insulating substance and thus presents no influenceover the measurement of the sheet resistivity. Further, the measurementof the resistivity was carried out directly in the form of a disksubstrate having a diameter of 120 mm by contacting the probes at aradial position of from 30 to 40 mm. In this manner, the measurement ofthe resistivity is carried out at a position which can be regarded as asubstantially infinitely large area.

On the basis of the resistivity R thus obtained, the sheet resistivityp, and the volume resistivity ρ_(s) were calculated by the followingformulae.ρ_(s) =F·R  (3)ρ_(v)=ρ_(s) ·t  (4)

Here, t is the film thickness. F is a correction coefficient determinedby the shape of the thin film region to be measured and usually takes avalue of from 4.3 to 4.5. Here, 4.4 was used.

Recording/retrieving evaluation was carried out by means of DDU1000tester manufactured by Pulsteck Co. (wavelength: about 780 nm, NA=0.5,spot shape: a circular of about 1.32 μm with an intensity of 1/e²,hereinafter this tester is referred to as tester 1) or DDU1000 testermanufactured by Pulsteck Co. (wavelength: about 780 nm, NA=0.5, spotshape: oval of about 1.43×1.33 μm with an intensity of 1/e², hereinafterthis tester will be referred to as tester 2). On the basis of thereference linear velocity of 1.2 m/s of CD being 1-time velocity,overwriting characteristics at from 8 to 32-times velocity wereevaluated.

The reference clock period of data at each linear velocity was oneinversely proportionated at each linear velocity against the referenceclock period 231 nsec of data at 1-time velocity.

Unless otherwise specified, retrieving was carried out at 1-timevelocity. The output signal from DDU1000 was passed through a highfrequency-passing filter having a cutoff lies between 5 and 20 kHz,whereupon the jitter was measured by a time interval analyzer(manufactured by Yokogawa Electric Corporation).

Modulation m₁₁ (=I₁₁/I_(top)) was read out by an inspection of the eyepattern on an oscilloscope. Further, R_(top) was separately obtained bycorrection by means of CD reference disk CD5B (sold by Philips Co.).

Formation of a logic level to control the recording pulse divisionmethod was carried out by means of an optional signal generator (AWG620or AWG710, manufactured by Sony Tektronix Co.). From the above signalgenerator, 2 channel gate signals comprising a logic signalcorresponding generally to one having G1, G2 and G3 in FIG. 5 integratedand a logic signal corresponding to G4, were taken out and, as ECL levellogic signals, input as gate signals against a laser driver of the abovetester.

EFM random data were overwritten ten times, whereupon the mark lengthsof the record data, the space lengths, the mark length and space lengthjitters, m₁₁, R_(top) and the asymmetry value were measured. With EFMrandom data, mark lengths and space lengths of from 3T to 11T randomlyappear. The frequencies of appearance of mark lengths relating to therespective n are about 34.0, 22.2, 16.4, 10.5, 4.9, 4.7, 4.4, 1.0 and1.9% with respect to n=3, 4, 5, 6, 7, 8, 9 and 11, respectively. Thefrequencies of appearance of the mark length and the space lengthrelating to the same n are substantially equal. They are average valuesof a data pattern appearing on a practical CD-ROM disk for data. Infact, 11T marks and spaces are used only as a pattern forsynchronization in most cases, and accordingly, the frequency ofappearance is small.

Further, unless otherwise specified, bias power Pb was made to be thesame as retrieving laser power Pr and constant at 0.8 mW.

In the measurement of the erase ratio by 3T/11T overwriting, a repeatingpattern (3T pattern) comprising a 3T mark and 3T space (between marks),was recorded ten times, then a repeating pattern (11T pattern)comprising 11T mark and 11T space (between marks), was overwritten,whereby the decreased amount (dB unit) of the carrier level of the 3Tmark was measured and taken as the erase ratio (erasability). Themeasurement of the carrier level was carried out by means of a spectrumanalyzer (TR4171) manufactured by Advantest or 8567A manufactured by HP,and the retrieving signal output of the tester was used as input. Theoverwriting was carried out at each linear velocity, but retrieving wasall carried out at a CD linear velocity (1.2 m/s). The resolution bandwidth of the spectrum analyzer was 30 kHz, and the video band width was30 Hz, and the input impedance was 50Ω.

Further, unless otherwise specified, evaluation of the overwritingcharacteristics was carried out after overwriting ten times (writing forthe first time in an unrecorded state, followed by overwriting ninetimes on the same track). Further, evaluation of the record signal afterthe accelerated aging test, was carried out only by retrieving thesignal overwritten ten times before the accelerated aging test, afterthe accelerated aging test.

Example 1

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 85 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 17.5 nm of a recording layer made ofGe₄Sb₈₂Te₁₄(Ge_(0.04)(Sb_(0.88)Te_(0.12))_(0.96)), 35 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 200 nm of a reflective layermade of Al_(99.5)Ta_(0.5) and about 4 μm of an ultraviolet-curable resinlayer, were formed in this order to obtain a rewritable compact disk.Here, the meaning of (ZnS)₈₀(SiO₂)₂₀ indicates that it is a filmobtained by high frequency sputtering of a target having 80 mol % of ZnSand 20 mol % of SiO₂ mixed. Further, the compositional ratio inGe₄Sb₈₂Te₁₄ or Al_(99.5)Ta_(0.5) is an atomic ratio. The same applies inthe following Examples. The volume resistivity ρ_(v) of thisAl_(99.5)Ta_(0.5) reflective layer was 80 nΩ·m, and the sheetresistivity ρ_(s) was about 0.4 Ω/□. The initialization was carried outby scanning a laser diode beam having a wavelength of about 810 nm andhaving an oval spot shape having a major axis of about 150 μm and aminor axis of about 1.0 μm, in the minor axis direction at a linearvelocity of about 2 m/s. The irradiation power was 950 mW.

On this disk, by means of the tester 1 with NA=0.50, overwriting of EFMmodulation signal was carried out at 24 and 10-times velocities, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 19 mW toabout 29 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Each was evaluated by the value afteroverwriting ten times.

In 24-times velocity recording, recording method CD1-1 was applied.Firstly, a case where T_(d1) and T_(d1)′ are constant irrespective of n,was studied, and in the following, this is designated as “recordingmethod CD1-1a”. “Recording method CD1-1a” is a practical usage whereinthe number of independent parameters in the recording pulse divisionmethod (II-A) is further limited.

Recording Method CD1-1a

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m−1),

β_(m−1)+α_(m)=2.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.35, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.4, provided that α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=0.9, α₁=α₁′=1.1, β₁=1, Δ₁=0.35, α_(i)=α_(i)′=αc =1(αc is constant with respect to i when i=2 to m−1), β_(m−1)=1,Δ_(m−1)=0, Δ_(m)=0.4, Δ_(mm)=0.4, α_(m)=1, and β_(m)=β_(m)′=0.4, andthey are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=0.9, α₁=1.1, β₁=1,α₂=1 and β_(m)=0.4,

with respect to 5T mark, T_(d1)′=0.9, α₁′=1.1, β₁′=1.35, α₂′=1.4 andβ_(m)′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.9, α₁′=1.6 andβ₁′=0.7.

On the other hand, in the case of 10-times velocity recording, thefollowing “Recording method CD2-1a” was used as a specific example ofrecording method CD2-1. “Recording method CD2-1a” is a practical usagewherein the number of independent parameters in the recording pulsedivision method (V) is further limited.

Recording Method CD2-1a

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β₁+α₂=1.8,

β_(i−1)+α_(i)=2 (i=3 to m−1)

β_(m−1)+α_(m)=2.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.2, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.55, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=Δ_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.5, α₁=α₁′=0.5, β₁=1.3, Δ₁=0.4,α_(i)=α_(i)′=αc=0.5 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.5, Δ_(m−1)=0.35, Δ_(m)=0.2, Δ_(mm)=0.55, α_(m)=0.5, andβ_(m)=β_(m)′=1.3, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.5, α₁=0.5, β₁=1.3,α₂=0.5 and β₂=1.3, and with respect to 5T mark, T_(d1)′=1.5, α₁′=0.5,β₂′=1.7, α₂′=0.8 and β₂′=1.6.

With respect to 3T mark, T_(d1)′=1.5, α₁′=0.8 and β₁′=2.

Then, the recording pulse division method (II-A) wherein T_(d1) andT_(d1)′ are not set to be constant for all n and set to have differentvalues with respect to 3T and 4T marks, was studied in recording at24-times velocity. The following recording method will be referred to asrecording method CD-IIa.

Recording Method CD-IIa

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark is divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β₁+α₂=1.95,

β_(i−1)+α_(i)=2 (i=3 to m−1),

β_(m−1)+α_(m)=1.95.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β₁′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁+α₂′=2.25, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)+α_(m)′=2.35, provided that α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, β₁=0.95, Δ₁=0.3, α_(i)=α_(i)=αc=1 (αcis constant with respect to i when i=2 to m−1), β_(m−1)=1, Δ_(m−1)=0,Δ_(m)=0.4, Δ_(mm)=0.4, α_(m)=0.95, and β_(m)=β_(m)′=0.3, and they areconstant when m is at least 3.

When m=2, with respect to 4T mark, T_(d1)=0.95, α₁=1, β₁=0.95, α₂=0.95and β₂=0.3, and with respect to 5T mark, T_(d1)′=1, α₁′=1, β₁′=1.25,α₂′=1.35 and β₂′=0.3.

Further, with respect to 3T mark, T_(d1)′=0.75, α₁′=1.9 and β₁′=0.3.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 1. Each recording method is based on the recordingpulse method (II-A) or (V), and therefore, in the case where m is atleast 3, ten parameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1),α_(m), Δ_(m) and β_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, inthe recording pulse division method (II), are presented. However,(T_(d1)′, α₁′ and β₁′) in the case where n=3 are presented in thecolumns for T_(d1), α₁ and β₁. (T_(d1), α₁, α₂ and β₂) in the case wheren=4 and (T_(d1)′, α₁′, β₁′, α₂′ and 8 2′) in the case where n=5 arepresented in the columns for T_(d1), α₁, β₁, α_(m) and β_(m). Here, inthe recording methods CD1-1a, CD2-1a and CD-IIa, β₁ and β₁′ in the casewhere n=4, 5 are equal to β₁ and β₁′ (=β₁+Δ₁) in the case where m is 3,respectively. TABLE 1 Recording method T_(d1) α₁ β₁ Δ₁ αc β_(m−1)Δ_(m−1) α_(m) Δ_(m) β_(m) CD1-1a m ≧ 3 0.9 1.1 1 0.35 1 1 0.1 1.4 0.40.4 n = 5 0.9 1.1 1.35 1.1 0.4 n = 4 0.9 1.1 0.7 1.05 0.4 n = 3 0.9 1.60.3 CD2-1a m ≧ 3 1.5 0.5 1.3 0.4 0.5 1.5 0.35 0.8 0.2 1.3 n = 5 1.5 0.51.7 0.55 1.6 n = 4 1.5 0.5 1.35 0.5 1.3 n = 3 1.5 0.8 2 CD-IIa m ≧ 3 1 11 0.35 1 1 0.9 3 0.4 0.3 n = 5 1 1 1.35 1.5 0.3 n = 4 0.95 1 1 1 0.3 n =3 1.7 9.1 0.25

The results of evaluation of overwriting characteristics in the cases of“Recording method CD1-1a” and “Recording method CD-IIa” at 24-timesvelocity, are shown in FIGS. 7 and 8. Pe/Pw i.e. the ratio of erasingpower Pe to writing power Pw was set to be 0.39 in “Recording methodCD1-1a” and 0.33 in “Recording method CD-IIa”. Pw was changed every 1 mWfrom 20 mW to about 27 mW. Bias power Pb was constant at 0.8 mW.

In the respective Figs., (a) to (f) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁(d)R_(top), (e) 3T mark length and (f) 3T space length, respectively.

The optimum writing power where the jitter becomes minimum, was from 23to 25 mW in “Recording method CD1-1a” and in the vicinity of from 23 to27 mW in “Recording method CD-IIa”, and the overwriting characteristicswere evaluated by the values at such a power.

The horizontal lines in FIGS. 7(a) and (b) and 8(a) and (b) indicate thestandardized upper limit value of jitter=35 (nsec) during retrieving at1-time velocity, and in the vicinity of the optimum Pw, good jittervalues of less than 35 nsec were obtained. Further, the jitters of othermark lengths and space lengths were also less than 35 nsec.

From FIGS. 7(c) and (d) and 8(c) and (d), it is evident that in eitherrecording method, the modulation m₁₁ was from 60% to 80% (from 0.6 to0.8), and R_(top) was from 15 to 25% (from 0.15 to 0.25).

In FIGS. 7(e) and (f) and 8(e) and (f), the horizontal solid linesindicate 3T mark length=3T space length=231×3 (nsec) during retrievingat 1-time velocity. Further, the horizontal dotted lines indicate 231nsec×3−40 nsec and 231 nsec×3+40 nsec. With respect to mark lengths andspace lengths, a deviation at a level of ±20% is usually allowable, andaccordingly, a deviation within ±30 to 40 nsec is allowable. From theFigs., it is evident that there is no substantial deviation of the marklengths and space lengths, and deviations, if any, are within theallowable range. Likewise, in the vicinity of the optimum Pw, also withrespect to the mark lengths and space lengths of from 4T to 11T, desiredmark lengths and space lengths were obtained within a range of thereference clock period T±0%.

Particularly, in 24-times velocity recording, when FIGS. 8(a) and (b)showing the results of overwriting characteristics of “Recording methodCD-IIa” where T_(d1) is not set to be constant, are compared with FIGS.7(a) and (b) showing the results of overwriting characteristics of“Recording method CD1-1a” where T_(d1) is set to be constant, it isapparent that in FIG. 8, the minimum value of the 3T space length jitteris 24.1 nsec which is lower than 26.9 nsec in FIG. 7, and the Pw rangewithin which the jitter is less than 35 nsec, is wider, indicating awider power margin.

FIG. 9 shows the results of “Recording method CD2-1a” at 10-timesvelocity. Pe/Pw i.e. the ratio of erasing power Pe to writing power Pwis made to be constant at 0.39, and Pw was changed every 1 mW from about19 mW to about 29 mW. Bias power Pb was constant at 0.8 W.

FIGS. 9(a) to (f) show the Pw dependency of (a) 3T mark length jitter,(b) 3T space length jitter, (c) modulation m₁₁, (d) R_(top), (e) 3T marklength and (f) 3T space length, respectively. While the optimum writingpower is in the vicinity of from 23 to 27 mW in 24-times velocityrecording, it is in the vicinity of from 22 to 27 mW in 10-timesvelocity recording, and the overwriting characteristics were alsoevaluated by the values at this power.

The horizontal lines in FIGS. 9(a) and (b) indicate the standardizedupper limit value of jitter=35 (nsec) during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, good jitter values ofless than 35 nsec were obtained. Further, the jitters of other marklengths and space lengths were also less than 35 nsec.

From FIGS. 9(c) and (d), it is evident that in either recording method,the modulation m₁₁ was from 60% to 80% (from 0.6 to 0.8), and R_(top)was from 15 to 25%.

In FIGS. 9(e) and (f), the horizontal solid lines indicate 3T marklength=3T space length=231×3 (nsec) during retrieving at 1-timevelocity. Further, the horizontal dotted lines indicate 231 nsec×3−40nsec and 231 nsec×3+40 nsec. With respect to mark lengths and spacelengths, a deviation of about ±20% is usually allowable, andaccordingly, a deviation within ±30 to 40 nsec is allowable. From theFigs., it is evident that there is no substantial deviation of the marklengths and space lengths, and deviations, if any, are within theallowable range. Likewise, in the vicinity of the optimum Pw, also withrespect to the mark lengths and space lengths of from 4T to 11T, desiredmark lengths and space lengths were obtained within a range of thereference clock period T±10%. As the asymmetry value, a value within±10% was obtained.

In summarizing the foregoing, good recording characteristics wereobtained at 10 and 24-times velocities, and if the recording medium andthe recording pulse division method (II-A) or (V) of the presentinvention are applied, good characteristics will be obtained also atlinear velocities between them, and the retrieving signals will be of aquality retrievable by conventional CD drives.

Now, the results of evaluation of overwriting durability will bedescribed in cases wherein “Recording method CD1-1a” and “Recordingmethod CD-IIa” at 24-times velocity, and “Recording method CD2-1a” at10-times velocity were used. The overwriting cycle dependency whenrepeated overwriting was carried out at Pe/Pw=9.4 mW/24 mW, 8.6 mW/26 mWand 9 mW/23 mW, is shown in FIGS. 10, 11 and 12, respectively. In therespective Figs., (a) shows 3T mark length jitter, and (b) shows 3Tspace length jitter. In FIGS. 10, 11 and 12, for the purpose of showingthe number of cycles of repeated overwriting on a logarithmic graph, thefirst recording is represented by first overwriting, and whenoverwriting was carried out nine times thereon, is represented by 10thoverwriting. Also in the following Examples, the number of cycles ofrepeated overwriting is shown in the same manner on a logarithmic axis.

At each linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW is sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. The3T/11T overwriting erase ratio was measured at 10-times velocity byusing 3T and 11T pulses of “Recording method CD2-1a”, and at 24-timesvelocity by using 3T and 11T pulses of “Recording method CD-IIa”. The3T/11T overwriting erase ratios at 10-times velocity and 24-timesvelocity were 29 and 26 dB, respectively and thus sufficient eraseratios were obtained at the respective linear velocities.

Further, disks recorded at 24-times velocity by “Recording methodCD1-1a” and “Recording method CD-IIa” were subjected to an acceleratedtest at 105° C., whereby even upon expiration of 3 hours, no substantialdeterioration of the recorded signals was observed. The jitter was foundto have increased by about 5 nsec, but still was lower than 35 nsec inretrieving at 1-time velocity, and the reflectivity R_(top) and themodulation m₁₁ also did not substantially decrease and maintained atleast 90% of the initial values.

Example 2

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 18 nm of a recording layer made ofIn₁₂Ge₈Sb₈₀(In_(0.12)(Ge_(0.09)Sb_(0.91))_(0.88)), 30 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 200 nm of a reflective layermade of Al_(99.5)Ta_(0.5) and about 4 μm of an ultraviolet-curable resinlayer, were formed in this order to obtain a rewritable compact disk.The volume resistivity ρ_(v) of this Al_(99.5)Ta_(0.5) reflective layerwas 80 nΩ·m, and the sheet resistivity ρ_(s) was about 0.4 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 75 μm and a minor axis of about 1.0 μm, at a linearvelocity of about 12 m/s. The irradiation power was 900 mW.

On this disk, by means of the tester 1 with NA=0.50, overwriting of EFMmodulation signal was carried out at 24 and 10-times velocities, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 21 mW toabout 30 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Pb was constant at 0.8 mW. Each wasevaluated by the value after overwriting ten times.

The recording pulse division method was as follows.

In 24-times velocity recording, recording method CD1-1 was applied.Firstly, a case where T_(d1) and T_(d1)′ are constant irrespective of n,was studied, and in the following, this is designated as “recordingmethod CD1-1b”. “Recording method CD1-1b” is a practical usage whereinthe number of independent parameters in the recording pulse divisionmethod (II-A) is further limited.

Recording Method CD1-1b

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m−1),

β_(m−1)+α_(m)=1.95.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.35, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.4, provided that α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=0.9, α₁=α₁′=1.1, β₁=1, Δ₁=0.35, α_(i)=α_(i)′=αc=1(αc is constant with respect to i when i=2 to m−1), β_(m−1)=0.9,Δ_(m−1)=0.1, Δ_(m)=0.35, Δ_(mm)=0.45, α_(m)=1.05, and β_(m)=β_(m)′=0.4,and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=0.9, α₁=1.1, β₁=0.9,α₂=1.05 and β_(m)=0.4. Here, β₁=0.9 in 4T mark is equal to β_(m−1) (β₂)in the case where m=3 (6T mark).

On the other hand, with respect to 5T mark, T_(d1)′=0.9, α₁′=1.1,β₁′=1.35, α₂′=1.4 and β_(m)′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.9, α₁′=1.8 andβ₁′=0.6.

On the other hand, in the case of 10-times velocity recording, thefollowing “Recording method CD2-1b” was used as recording method CD2-1.“Recording method CD2-1b” is a practical usage wherein the number ofindependent parameters in the recording pulse division method (V) isfurther limited.

Recording Method CD2-1b

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β₁+α₂=2,

β_(i−1)+α_(i)=2 (i=3 to m−1)

β_(m−1)+α_(m)=1.95.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β₁′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.4, provided that β₁′=β₁Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.55, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.5, α₁=α₁′=0.5, β₁=1.5, Δ₁=0.4,α_(i)=α_(i)′=αc=0.5 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.45, Δ_(m−1)=0.45, Δ_(m)=0.15, Δ_(mm)=0.6, α_(m)=0.5, andβ_(m)=β_(m)′=1.2, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.5, α₁=0.5, β₁=1.45,α₂=0.5 and β₂=1.2. Here, β₁=1.45 in 4T mark is equal to β₂(β_(m−1)) inthe case where m=2 (n=6T mark).

On the other hand, with respect to 5T mark, T_(d1)′=1.5, α₁′=0.5,β₁′=1.9, α₂′=0.65 and β₂′=1.6.

With respect to 3T mark, T_(d1)′=1.5, α₁′=0.8 and β₁′=2.

Then, the recording pulse division method (II-A) wherein T_(d1) andT_(d1)′ are not set to be constant for all n and set to have differentvalues with respect to 3T and 4T marks, was studied in recording at24-times velocity by the following recording method CD-IIb.

Recording Method CD-IIb

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark is divided into m sections, and α_(i) and β_(i)′ inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m−1),

β_(m−1)+α_(m)=1.9.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.35, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.4, provided that α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, β₁=1, Δ₁=0.35, α_(i)=α_(i)′=αc=1 (αcis constant with respect to i when i=2 to m−1), β_(m−1)=0.9,Δ_(m−1)=0.1, Δ_(m)0.4, Δ_(mm)=0.5, α_(m)=1, and β_(m)=β_(m)′=0.3, andthey are constant when m is at least 3.

When m=2, with respect to 4T mark, T_(d1)=0.95, α₁=1, β₁=1, β₂=1and/2=0.3, and with respect to 5T mark, T_(d1)′=1, α₁′=1, β₂′=1.35,α₂′=1.4 and β₂′=0.3.

Further, with respect to 3T mark, T_(d1)′=0.5, α₁′=2.4 and β₁′=0.45.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 2. Each recording method is based on the recordingpulse method (II-A) or (V), and therefore, in the case where m is atleast 3, ten parameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1),α_(m), Δ_(m) and β_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, inthe recording pulse division method (II), are presented. However,(T_(d1)′, α₁′ and β₁′) in the case where n=3 are presented in thecolumns for T_(d1), α₁ and β₁. (T_(d1), α₁, β₁, α₂ and β₂) in the casewhere n=4 and (T_(d1)′, α₁′, β₁, α₂′ and β₂′) in the case where n=5 arepresented in the columns for T_(d1), α₁, β₁, α_(m) and β_(m). Here, inthe recording methods CD1-1b and 2-1b, β₁ in the case where n=4, isequal to β_(m−1) in the case where m is at least 3 (n=≧6), and β₁′ inthe case where n=5, is equal to β₁′ (=β₁+Δ₁) in the case where m is atleast 3 (n≧6). In the recording method IIb, β₁ and β₁′ in the case wheren=4, 5 are equal to β₁ and β₁′ (=β₁+Δ₁) in the case where m is 3,respectively. TABLE 2 Recording method T_(d1) α₁ β₁ Δ₁ αc β_(m−1)Δ_(m−1) α_(m) Δ_(m) β_(m) CD1-1b m ≧ 3 0.9 1.1 1 0.35 1 0.9 0.1 1.050.35 0.4 n = 5 0.9 1.1 1.35 1.4 0.4 n = 4 0.9 1.1 0.9 1.05 0.4 n = 3 0.91.8 0.6 CD2-1b m ≧ 3 1.5 0.5 1.5 0.4 0.5 1.45 0.45 0.5 0.15 1.2 n = 51.5 0.5 1.9 0.65 1.6 n = 4 1.5 0.5 1.45 0.5 1.2 n = 3 1.5 0.8 2 CD-IIb m≧ 3 1 1 1 0.35 1 0.9 0.1 1 0.4 0.3 n = 5 1 1 1.35 1.4 0.3 n = 4 0.95 1 11 0.3 n = 3 0.5 24 0.45

The results of evaluation of overwriting characteristics are shown inFIGS. 13 and 14 in the cases of “Recording method CD1-1b” and “Recordingmethod CD-IIb” at 24-times velocity, and in FIG. 15 in the case of“Recording method CD2-1b” at 10-times velocity. Pe/Pw i.e. the ratio oferasing power Pe to writing power Pw was set to be 0.35 in “Recordingmethod CD1-1b” and 0.33 in “Recording method CD-IIb” at 24-timesvelocity, and 0.31 in “Recording method CD2-1b” at 10-times velocity. Pwwas changed every 1 mW from 21 mW to about 30 mW. Bias power Pb wasconstant at 0.8 mW.

In the respective Figs., (a) to (f) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁, (d)R_(top), (e) 3T mark length and (f) 3T space length, respectively.

The optimum writing power was in the vicinity of from 25 to 27 mW in“Recording method CD1-1b” and in the vicinity of from 24 to 28 mW in“Recording method CD-IIb” in the 24-times velocity recording, and in thevicinity of from 23 to 28 mW in the 10-times velocity recording, and theoverwriting characteristics were evaluated by the values at such apower.

The horizontal lines in (a) and (b) in FIGS. 13, 14 and 15 indicate thestandardized upper limit value of jitter=35 (nsec) during retrieving at1-time velocity. Good jitter values of less than 35 nsec were obtainedat any linear velocity.

From (c) and (d) in FIGS. 13, 14 and 15, it is evident that at anylinear velocity, the modulation m₁₁ was from 60% to 80% (from 0.6 to0.8), and R_(top) was from 15 to 25%.

Then, 3T mark lengths and 3T space lengths during retrieving at 1-timevelocity were measured in the cases where recording was carried out by“Recording method CD1-1b”, “Recording method CD-IIb” and “Recordingmethod CD2-1b”. In either recording method, 3T mark lengths and 3T spacelengths were within a range of a deviation of about ±10% from 23/nsec×3.Specifically, in FIG. 14(e) and (f), the horizontal solid lines indicate3T mark length=3T space length=231×3 (nsec) during retrieving at 1-timevelocity. Further, the horizontal dotted lines indicate 231 nsec×3−40nsec and 231 nsec×3+40 nsec. With respect to mark lengths and spacelengths, a deviation of about ±20% from the reference clock period T isusually allowable, and accordingly, a deviation within ±30 to 40 nsec isallowable. From FIGS. 14 (e) and (f), it is evident that there is nosubstantial deviation of the mark lengths and space lengths, anddeviations, if any, are within the allowable range.

Likewise, in the vicinity of the optimum Pw, also with respect to themark lengths and space lengths of from 4T to 11T, desired mark lengthsand space lengths were obtained within a range of the reference clockperiod T±10%. As the asymmetry value, a value within ±10% was obtained.

In summarizing the foregoing, good recording characteristics wereobtained at 10 and 24-times velocities, and the retrieving signals wereof a quality retrievable by conventional CD drives. Further, byadjusting the pulses, good characteristics will be obtained also atlinear velocities between them.

Now, the results of evaluation of overwriting durability will bedescribed in cases wherein “Recording method CD1-1b” and “Recordingmethod CD-IIb” at 24-times velocity, and “Recording method CD2-1b” at10-times velocity were used. When repeated overwriting was carried outat Pw/Pe=25 mW/8.8 mW, 26 mW/8.6 mW and 26 mW/8.1 mW, respectively, ateach linear velocity, the overwriting durability of 1000 cycles requiredfor CD-RW was sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. The3T/11T overwriting erase ratio was measured at 10-times velocity byusing 3T and 11T pulses of “Recording method CD2-1b”, and at 24-timesvelocity by using 3T and 11T pulses of “Recording method CD-IIb”. The3T/11T overwriting erase ratios at 10-times velocity and 24-timesvelocity were 28 and 21 dB, respectively, and thus sufficient eraseratios were obtained at the respective linear velocities.

Further, disks recorded at 24-times velocity by “Recording methodCD1-1b” and “Recording method CD-IIb” were subjected to an acceleratedtest at 105° C., whereby even upon expiration of 3 hours, no substantialdeterioration of the recorded signals was observed. The jitter was foundto have changed by about 2 nsec, but still was lower than 35 nsec inretrieving at 1-time velocity, and the reflectivity R_(top) and themodulation m₁₁ also did not substantially decrease and maintained atleast 90% of the initial values.

Example 3

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 15 nm of a recording layer made ofSn₂₀Ge₁₈Sb₆₂(Sn_(0.2)(Ge_(0.23)Sb_(0.77))_(0.8)), 30 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 200 nm of a reflective layermade of Al_(99.5)Ta_(0.5) and about 4 μm of an ultraviolet-curable resinlayer, were formed in this order to obtain a rewritable compact disk.The volume resistivity ρ_(v) of this Al_(99.5)Ta_(0.5) reflective layerwas 80 nΩ·m, and the sheet resistivity ρ_(s) was about 0.4 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 150 μm and a minor axis of about 1.0 μm, at a linearvelocity of about 12 m/s. The irradiation power was 1600 mW.

On this disk, by means of the tester 1 with NA=0.50, overwriting of EFMmodulation signal was carried out at 24 and 10-times velocities, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 21 mW toabout 30 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Pb was constant at 0.8 mW. Each wasevaluated by the value after overwriting ten times.

The recording pulse division method was as follows.

In 24-times velocity recording, recording method CD1-1 was applied, thisis designated as “recording method CD1-1c”. “Recording method CD1-1c” isa practical usage wherein the number of independent parameters in therecording pulse division method (II-A) is further limited.

Recording Method CD1-1c

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.35, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.45, provided that β_(m−1)′=β_(m−1)+Δ_(m−1),α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁=1, β₁=1, Δ₁=0.35, α_(i)=α₁′=αc=1 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.0, Δ_(m−1)=0,Δ_(m)=0.5, Δ_(mm)=0.5, α_(m)=0.95, and β_(m)=β_(m)′=0.3, and they areconstant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1, α₁=1, β₁=1,α₂=0.95 and β_(m)0.3,

with respect to 5T mark, T_(d1)′=1, α₁′=1, β₁=1.35, α₂′=1.45 andβ_(m)′=0.3.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.75, α₂′=1.95 andβ_(m)′=0.5.

On the other hand, in the case of 10-times velocity recording, thefollowing “Recording method CD2-1c” was used as recording method CD2-1.“Recording method CD2-1c” is a practical usage wherein the number ofindependent parameters in the recording pulse division method (V) isfurther limited.

Recording Method CD2-1c

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α_(i)=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁=2,

β₁′+α₂′=2.4, provided that β₁′=β₁Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.55, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.5, α₁=α₁′=0.5, β₁ =1.6, Δ₁=0.4,α_(i)=α_(i)′=αc=0.4 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.6, Δ_(m−1)=0.35, Δ_(m)=0.2, Δ_(mm)=0.55, α_(m)=0.4, andβ_(m)=β_(m)′=1.1, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.5, α₁=0.5, β₁=1.6,α₂=0.4 and β₂=1.1, and with respect to 5T mark, T_(d1)′=1.5, α₁′=0.5,β₁′=2, α₂′=0.6 and β₂′=1.45. Here, β₂′=1.45 in 5T mark is one having0.35 imparted to β₃′(β_(m)′)=1.1 where m=3 (6T mark).

With respect to 3T mark, T_(d1)′=1.5, α₁=0.6 and β₁′=2.1.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 3. Each recording method is based on the recordingpulse method (II-A) or (V), and therefore, in the case where m is atleast 3, ten parameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1),α_(m), Δ_(m) and β_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, inthe recording pulse division method (II-A), are presented. However,(T_(d1)′, α₁′ and β₁′) in the case where n=3 are presented in thecolumns for T_(d1), α₁ and β₁. (T_(d1), α₁, β₁, α₂ and β₂) in the casewhere n=4 and (T_(d1)′, α₁′, β₁′, α₂′ and β₂′) in the case where n=5 arepresented in the columns for T_(d1), α₁,β₁, α_(m) and β_(m). Here, inthe recording methods CD1-1c and CD2-1c, β₁ and β₁′ in the case wheren=4, 5 are equal to β₁ and β₁′ (=β₁+Δ₁) in the case where m is 3,respectively. TABLE 3 Recording method T_(d1) α₁ β₁ Δ₁ αc β_(m−1)Δ_(m−1) α_(m) Δ_(m) β_(m) CD1-1c m ≧ 3 1 1 1 0.35 1 1 0 0.95 0.5 0.3 n =5 1 1 1.35 1.45 0.3 n = 4 1 1 1 0.95 0.3 n = 3 0.75 1.95 0.5 CD2-1c m ≧3 1.5 0.5 1.6 0.4 0.4 1.6 0.35 0.4 0.2 1.1 n = 5 1.5 0.5 2 0.6 1.45 n =4 1.5 0.5 1.6 0.4 1.1 n = 3 1.5 0.6 2.1

The results of evaluation of overwriting characteristics are shown inFIG. 18 in the case of “Recording method CD1-1c” at 24-times velocityand in FIG. 19 in the case of “Recording method CD2-1c” at 10-timesvelocity. Pe/Pw i.e. the ratio of erasing power Pe to writing power Pwwas set to be 0.31 in “Recording method CD1-1c” at 24-times velocity and0.33 in “Recording method CD2-1c” at 10-times velocity. Pw was changedevery 1 mW from about 21 mW to about 30 mW. Bias power Pb was constantat 0.8 mW.

In the respective Figs., (a) to (f) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁, (d)R_(top), (e) 3T mark length and (f) 3T space length, respectively.

The optimum writing power was in the vicinity of from 25 to 28 mW in“Recording method CD1-1c” at 24-times velocity and in the vicinity offrom 24 to 30 mW in “Recording method CD2-1c” at 10-times velocity, andthe overwriting characteristics were evaluated by the values at such apower.

The horizontal lines in FIGS. 18(a) and (b) and 19(a) and (b) indicatethe standardized upper limit value of jitter=35 (nsec) during retrievingat 1-time velocity. Good jitter values of less than 35 nsec wereobtained at any linear velocity.

From FIGS. 18(c) and (d) and 19(c) and (d), it is evident that at anylinear velocity, the modulation m₁₁ was from 60% to 80% (from 0.6 to0.8), and R_(top) was from 15 to 25%.

Then, 3T mark lengths and 3T space lengths during retrieving at 1-timevelocity were measured in the cases where recording was carried out by“Recording method CD1-1c” and “Recording method CD2-1c”. In eitherrecording method, 3T mark lengths and 3T space lengths were within arange of a deviation of about ±10% from 23/nsec×3 nsec. Specifically, inFIGS. 18(e) and (f) and 19(e) and (f), the horizontal solid linesindicate 3T mark length=3T space length=231×3 (nsec) during retrievingat 1-time velocity. Further, the horizontal dotted lines indicate 231nsec×3−40 nsec and 231 nsec×3+40 nsec. With respect to mark lengths andspace lengths, a deviation of about ±20% from the reference clock periodT is usually allowable, and accordingly, a deviation within ±30 to 40nsec is allowable. From FIGS. 18(e) and (f) and 19(e) and (f), it isevident that there is no substantial deviation of the mark lengths andspace lengths, and deviations, if any, are within the allowable range.

Likewise, in the vicinity of the optimum Pw, also with respect to themark lengths and space lengths of from 4T to 11T, desired mark lengthsand space lengths were obtained within a range of the reference clockperiod T±10%. As the asymmetry value, a value within ±10% was obtained.

In summarizing the foregoing, good recording characteristics wereobtained at 10 and 24-times velocities, and the retrieving signals wereof a quality retrievable by conventional CD drives. Further, byadjusting the pulses, good characteristics will be obtained also atlinear velocities between them.

Now, the results of evaluation of overwriting durability will bedescribed in cases wherein “Recording method CD1-1c” at 24-timesvelocity, and “Recording method CD2-1c” at 10-times velocity were used.When repeated overwriting was carried out at Pw/Pe=26 mW/8.1 mW and 27mW/8.9 mW, respectively, at each linear velocity, the overwritingdurability of 1000 cycles required for CD-RW was sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. The3T/11T overwriting erase ratio was measured at 10-times velocity byusing 3T and 11T pulses of “Recording method CD2-1c”, and at 24-timesvelocity by using 3T and 11T pulses of “Recording method CD1-1c”. The3T/11T overwriting erase ratios at 10-times velocity and 24-timesvelocity were 33 and 21 dB, respectively, and thus sufficient eraseratios were obtained at the respective linear velocities.

Further, disks recorded at 24-times velocity by “Recording methodCD1-1c” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to have changed by about 2nsec, but still was lower than 35 nsec in retrieving at 1-time velocity,and the reflectivity R_(top) and the modulation m₁₁ also did notsubstantially decrease and maintained at least 90% of the initialvalues.

Example 4

Using the disk of the above Example 3 and the tester 1, in 24-timesvelocity recording, recording method CD1-2 was applied, and this isdesignated as “recording method CD1-2a”. “Recording method CD1-2a” is apractical usage wherein the number of independent parameters in therecording pulse division method (III-A) is further limited.

Recording Method CD1-2a

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.85, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m−1)′α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, α_(i)=α_(i)′=αc=1 (αc is constant withrespect to i when i=2 to m−1), β_(m−1)=1, Δ_(m−1)=0.4, Δ_(m)=0.45,Δ_(mm)=0.85, α_(m)=1, β_(m)=0.3 and Δ_(m)′=0, and they are constant whenm is at least 2.

However, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in the case where m=2(n=4, 5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′),α₃(α_(m)), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3,respectively.

Namely, with respect to 4T mark, α₁=1, β₁=1, α₂=1 and β₂=0.3, and withrespect to 5T mark, α₁′=1, β₁′=1.4, α₂′=1.45 and β₂′=0.3.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.9, α₁′=1.6 andβ₁′=0.55.

On the other hand, in the case of 10-times velocity recording, thefollowing “Recording method CD2-2a” was used as recording method CD2-2.“Recording method CD2-2a” is a practical usage wherein the number ofindependent parameters in the recording pulse division method (VI) isfurther limited.

Recording Method CD2-2a

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1)

β_(m−1)′+α_(m)′=2.55, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.5, α₁=α₁′=0.5, α_(i)=α₁′=αc=0.4 (αc is constantwith respect to i when i=2 to m−1), β_(m−1)=1.6, Δ_(m−1)=0.35,Δ_(m)=0.2, Δ_(mm)=0.55, α_(m)=0.4, β_(m)=0.8 and Δ_(m)′=0.4, and theyare constant when m is at least 2.

However, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in the case where m=2(n=4, 5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′),α₃(α_(m)), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3,respectively.

Namely, with respect to 4T mark, α₁=0.5, α₁=1.6, α₂=0.4 and β₂=0.8, andwith respect to 5T mark, α₁′=0.5, β₁′=1.95, α₂′=0.6 and β₂′=1.2.

With respect to 3T mark, T_(d1)′=1.5, α₁′=0.7 and β₁′=1.7.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 4.

In Table 4, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 4, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, in the recordingpulse division method (III-A), T_(d1)+α₁=T_(d1)′+α₁′=2,β_(m−1)+α₂=β_(m−1)+α_(m)=2, α₁=α_(m)=αc and Δ_(m) were set to beconstant irrespective of m. Therefore, although 10 parameters arepresented in Table 4 including T_(d1), β₁, β_(m−1), β_(m) and α_(m),independent parameters are 5 i.e. α₁, αc, Δ_(m−1), Δ_(m) and Δ_(m)′.Further, when n=4, β₁=β_(m−1) =βc, α ₂=α_(m)=αc and β=β_(m). When n=5,β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), and β₂′=β_(m)+Δ_(m)′. TABLE 4 Recordingmethod T_(d1) α₁ β₁ αc β_(m−1) Δ_(m−1) α_(m) Δ_(m) β_(m) Δ_(m)′ CD1-2a n= 3 0.9 1.6 0.55 n = 4˜11 1 1 1 1 1 0.4 1 0.45 0.3 0 CD2-2a n = 3 1.50.7 1.7 n = 4˜11 1.5 0.5 1.6 0.4 1.6 0.35 0.4 0.2 0.8 0.4

The results of evaluation of overwriting characteristics are shown inFIG. 22 in the case of “Recording method CD1-2a” at 24-times velocityand in FIG. 23 in the case of “Recording method CD2-2a” at 10-timesvelocity. Pe/Pw i.e. the ratio of erasing power Pe to writing power Pwwas set to be constant at 0.30 in “Recording method CD1-2a” at 24-timesvelocity and at 0.30 in “Recording method CD2-2a” at 10-times velocity.In “Recording method CD1-2a”, Pw was changed every 1 mW from about 22 mWto about 30 mW. In “Recording method CD2-2a”, Pw was changed every 1 mWfrom about 20 mW to about 29 mW. Bias power Pb was constant at 0.8 mW.

In the respective Figs., (a) to (f) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁, (d)R_(top), (e) 3T mark length and (f) 3T space length, respectively.

The optimum writing power was in the vicinity of from 24 to 28 mW in“Recording method CD1-2a” at 24-times velocity and in the vicinity offrom 23 to 28 mW in “Recording method CD2-2a” at 10-times velocity, andthe overwriting characteristics were evaluated by the values at such apower.

The horizontal lines in FIGS. 22(a) and (b) and 23(a) and (b) indicatethe standardized upper limit value of jitter=35 (nsec) during retrievingat 1-time velocity. Good jitter values of less than 35 nsec wereobtained at any linear velocity.

From FIGS. 22(c) and (d) and 23(c) and (d), it is evident that at anylinear velocity, the modulation m₁₁, was from 60% to 80% (from 0.6 to0.8), and R_(top) was from 15 to 25%.

Then, 3T mark lengths and 3T space lengths during retrieving at 1-timevelocity were measured in the cases where recording was carried out by“Recording method CD1-2a” and “Recording method CD2-2a”. In eitherrecording method, 3T mark lengths and 3T space lengths were within arange of a deviation of about ±10% from 231 nsec×3 nsec. Specifically,in FIGS. 22(e) and (f) and 23 (e) and (f), the horizontal solid linesindicate 3T mark length=3T space length=231×3 (nsec) during retrievingat 1-time velocity. Further, the horizontal dotted lines indicate 231nsec×3−40 nsec and 231 nsec×3+40 nsec. With respect to mark lengths andspace lengths, a deviation of about ±20% from the reference clock periodT is usually allowable, and accordingly, a deviation within ±30 to 40nsec is allowable. From the FIGS. 22(e) and (f) and 23(e) and (f), it isevident that there is no substantial deviation of the mark lengths andspace lengths, and deviations, if any, are within the allowable range.

Likewise, in the vicinity of the optimum Pw, also with respect to themark lengths and space lengths of from 4T to 11T, desired mark lengthsand space lengths were obtained within a range of the reference clockperiod T±b 10%. As the asymmetry value, a value within ±10% wasobtained.

In summarizing the foregoing, good recording characteristics wereobtained at 10 and 24-times velocities, and the retrieving signals wereof a quality retrievable by conventional CD drives. Further, byadjusting the pulses, good characteristics will be obtained also atlinear velocities between them.

Now, the results of evaluation of overwriting durability will bedescribed in cases wherein “Recording method CD1-2a” at 24-timesvelocity, and “Recording method CD2-2a” at 10-times velocity were used.The overwriting cycle dependency when repeated overwriting was carriedout at Pw/Pe=26 mW/7.8 mW and 24 mW/7.2 mW is shown in FIGS. 24 and 25,respectively. In the respective Figs., (a) shows 3T mark length jitter,and (b) shows 3T space length jitter.

At each linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW is sufficiently satisfied.

Further, disks recorded at 24-times velocity by “Recording methodCD1-2a” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to have changed by about 2nsec, but still was lower than 35 nsec in retrieving at 1-time velocity,and the reflectivity R_(top) and the modulation m₁₁ also did notsubstantially decrease and maintained at least 90% of the initialvalues.

Example 5

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 15 nm of a recording layer made ofGe₁₅Sb₆₅Sn₂₀(Sn₂₀(Ge_(0.19)Sb_(0.81))_(0.8)), 27 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 3 nm of an interfacial layermade of SiO₂, 200 nm of a reflective layer made of Ag and about 4 μm ofan ultraviolet-curable resin layer, were formed in this order to obtaina rewritable compact disk. The volume resistivity ρ_(v) of this Agreflective layer was 24 nΩ·m, and the sheet resistivity ρ_(s) was about0.12 Ω/□. The initialization was carried out by scanning a laser diodebeam having a wavelength of about 810 nm and having an oval spot shapehaving a major axis of about 150 μm and a minor axis of about 1.0 μm, inthe minor axis direction at a linear velocity of about 12 m/s. Theirradiation power was 1650 mW.

On this disk, by means of the tester 1 with NA=0.50, overwriting of EFMmodulation signal was carried out at 32, 24 and 10-times velocities, andthe characteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 19 mW toabout 30 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Each was evaluated by the value afteroverwriting ten times.

In 32-times velocity recording, recording method CD1-1 was applied, thisis designated as “Recording method CD1-1d”. “Recording method CD1-1d” isa practical usage wherein the number of independent parameters in therecording pulse division method (II-A) is further limited.

Recording Method CD1-1d

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α1=2,

β₁+α₂=2,

β_(i−1)+α_(i)=2 (i=3 to m−1),

β_(m−1)+α_(m)=2.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.32, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.44, provided that β_(m−1)+′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, β₁=1.06, Δ₁=0.32, α_(i)=α_(i)′=αc=0.94(αc is constant with respect to i when i=2 to m−1), β_(m−1)=1.06,Δ_(m−1)=0, Δ_(m)=0.44, Δ_(m)=0.44, α_(m)=0.94, and β_(m)=β_(m)′=0.44,and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1, α₁1=1, β₁=1.06,α₂=0.94 and β₂=0.44, and with respect to 5T mark, T_(d1)′=1, α₁′=1,β₁′=1.38, α₂′=1.38 and β_(m)′=0.44.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.81, α₁′=1.91 andβ₁′=0.25.

Then, in the case of 24-times velocity recording, the following“Recording method CD2-1d” was used as a specific example of recordingmethod CD2-1. “Recording method CD2-1d” is a practical usage wherein thenumber of independent parameters in the recording pulse division method(V) is further limited.

Recording Method CD2-1d

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β₁+α₂=1.85,

β_(i−1)+α_(i)=2 (i=2 to m).

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.35, provided that β₂′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.3, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.3, α₁=α₁′=0.7, β₁=1.15, Δ₁=0.5,α_(i)=α_(i)′=αc=0.7 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.3, Δ_(m−1)=0.15, Δ_(m)=0.15, Δ_(mm)=0.3, α_(m)=0.7, andβ_(m)=Δ_(m)′=0.7, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.3, α₁=0.7, β₁=1.15,α₂=0.7 and β₂=0.7, and with respect to 5T mark, T_(d1)′=1.3, α₁′=0.7,β₁′=1.65, α₂′=1.05 and β₂′=0.7. Here, α₂′=1.05 is one having 0.2 addedto α₃′ (α_(m)′=α_(m)+Δ_(m)=0.7+0.15=0.85) where m=3 (6T mark).

With respect to 3T mark, T_(d1)′=1.3, α₁′=1.1 and β₁=0.95.

Further, in the case of 10-times velocity recording, the following“Recording method CD2-1e” was used as a specific example of recordingmethod CD2-1. “Recording method CD2-1e” is a practical usage wherein thenumber of independent parameters in the recording pulse division method(V) is further limited.

Recording Method CD2-1e

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2

β₁+α₂=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.3, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.3, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.7, α₁=α₁′=0.3, β₁=1.7, Δ₁=0.3,α_(i)=α_(i)′=αc=0.3 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.7, Δ_(m−1)=0.35, Δ_(m)=0.15, Δ_(mm)=0.45, α_(m)=0.3, andβ_(m)=β_(m)′=1.2, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.7, α₁=0.3, β₁=1.7,α₂=0.3 and β₂=1.2, and with respect to 5T mark, T_(d1)′=1.7, α₁′=0.3,β₁′=2, α₂′=0.45 and β₂′=1.65. Here, β₂′=1.65 is one having 0.45 added toβ₃′ (β_(m)′=1.2) where m=3 (6T mark).

With respect to 3T mark, T_(d1)′=1.7, α₁′=0.5 and β₁′=1.9.

Further, T_(d1), α_(i), β_(i), etc. in each recording method aresummarized in Table 5. Each recording method is based on the recordingpulse method (II) or (V), and therefore, in the case where m is at least3, ten parameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1), α_(m),Δ_(m) and β_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, in therecording pulse division method (II-A), are presented. However,(T_(d1)′, α₁′ and β₁′) in the case where n=3 are presented in thecolumns for T_(d1), α₁ and β₁. (T_(d1), α₁, β₁, α₂ and β₂) in the casewhere n=4 and (T_(d1)′, α₁′, β₁′, α₂′ and β₂′) in the case where n=5 arepresented in the columns for T_(d1), α₁, β₁, α_(m) and β_(m).

Here, in the recording methods CD1-1d, 2-1d and 2-1e, β₁ and β₁′ in thecase where n=4, 5 are equal to β₁ and β₁′ (=β₁+Δ₁) in the case where mis 3, respectively. TABLE 5 Recording method T_(d1) α₁ β₁ Δ₁ αc β_(m−1)Δ_(m−1) α_(m) Δ_(m) β_(m) CD1-1d m ≧ 3 1 1 1.06 0.32 0.94 1.06 0 0.940.44 0.44 n = 5 1 1 1.38 1.38 0.44 n = 4 1 1 1.06 0.94 0.44 n = 3 0.811.94 0.25 CD2-1d m ≧ 3 1.3 0.7 1.15 0.5 0.7 1.3 0.15 0.7 0.15 0.7 n = 51.3 0.7 1.65 1.05 0.7 n = 4 1.3 0.7 1.15 0.7 0.7 n = 3 1.3 1.1 0.95CD2-1e m ≧ 3 1.7 0.3 1.7 0.3 0.3 1.7 0.35 0.3 0.15 1.2 n = 5 1.7 0.3 20.45 1.65 n = 4 1.7 0.3 1.7 0.3 1.2 n = 3 1.7 0.5 1.9

The results of evaluation of overwriting characteristics are shown inFIGS. 26, 27 and 28 in the cases of “Recording method CD1-1d” at32-times velocity, “Recording method CD2-1d” at 24-times velocity and“Recording method CD2-1e” at 10-times velocity. Pe/Pw i.e. the ratio oferasing power Pe to writing power Pw was set to be constant at 0.30 in“Recording method CD1-1d”, 0.30 in “Recording method CD2-1d” and 0.30 in“Recording method CD2-1e”. In “Recording method CD1-1d”, Pw was changedevery 1 mW from 26 mW to about 30 mW. In “Recording method CD2-1d”, Pwwas changed every 1 mW from 23 mW to about 30 mW. In “Recording methodCD2-1e”, Pw was changed every 1 mW from 22 mW to about 30 mW. Bias powerPb was constant at 0.8 mW.

In the respective Figs., (a) to (f) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁, (d)R_(top), (e) 3T mark length and (f) 3T space length, respectively.

The optimum writing power where the jitter becomes minimum, was from 28to 30 mW in “Recording method CD1-1d” at 32-times velocity, from 25 to30 mW in “Recording method CD2-1d” at 24-times velocity and in thevicinity of from 25 to 30 mW in “Recording method CD2-1e” at 10-timesvelocity, and the overwriting characteristics were evaluated by thevalues at such a power.

The horizontal lines in (a) and (b) in FIGS. 26, 27 and 28 indicate thestandardized upper limit value of jitter=35 (nsec) during retrieving at1-time velocity, and in the vicinity of the optimum Pw, good jittervalues of less than 35 nsec were obtained. Further, the jitters of othermark lengths and space lengths were also less than 35 nsec.

From (c) and (d) in FIGS. 26, 27 and 28, it is evident that in eitherrecording method, the modulation m₁₁ was from 60% to 80% (from 0.6 to0.8), and R_(top) was from 15 to 25%.

In (e) and (f) in FIGS. 26, 27 and 28, the horizontal solid linesindicate 3T mark length=3T space length=231×3 (nsec) during retrievingat 1-time velocity. Further, the horizontal dotted lines indicate 231nsec ×3−40 nsec and 231 nsec×3+40 nsec. With respect to mark lengths andspace lengths, a deviation of about ±20% from the reference clock periodT is usually allowable, and accordingly, a deviation within ±30 to 40nsec is allowable. From the Figs., it is evident that in the vicinity ofthe optimum Pw, there is no substantial deviation of the mark lengthsand space lengths, and deviations, if any, are within the allowablerange. Likewise, in the vicinity of the optimum Pw, also with respect tothe mark lengths and space lengths of from 4T to 11T, desired marklengths and space lengths were obtained within a range of the referenceclock period T±10%. As the asymmetry value, a value within ±10% wasobtained.

If the recording medium and the recording method of this Example areemployed, good recording characteristics will be obtained at leastwithin a range of from 32-times velocity to 10-times velocity, and theretrieving signals will be of a quality retrievable by conventional CDdrives.

Now, the results of evaluation of overwriting durability Will bedescribed in cases wherein “Recording method CD1-1d” at 32-timesvelocity, “Recording method CD2-1d” at 24-times velocity, and “Recordingmethod CD2-1e” at 10-times velocity were used. The overwriting cycledependency when repeated overwriting was carried out at Pw/Pe=29 mW/8.7mW, 28 mW/8.4 mW and 27 mW/8.1 mW, is shown in FIGS. 29, 30 and 31,respectively. In the respective Figs., (a) shows 3T mark length jitter,and (b) shows 3T space length jitter.

At any linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW is sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. The3T/11T overwriting erase ratio was measured at 10-times velocity byusing 3T and 11T pulses of “Recording method CD2-1e”, at 24-timesvelocity by using 3T and 11T pulses of “Recording method CD2-1d”, and at32-times velocity using 3T and 11T pluses of “Recording method CD1-1d”.The 3T/11T overwriting erase ratios at 10-times velocity, 24-timesvelocity and 32-times velocity were 30, 28 and 24 dB, respectively, andthus sufficient erase ratios were obtained at the respective linearvelocities.

Further, disks recorded at 32-times velocity by “Recording methodCD1-1d” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to have changed by about 2nsec, but still was lower than 35 nsec in retrieving at 1-time velocity,and the reflectivity R_(top) and the modulation m₁₁ also did notsubstantially decrease and maintained at least 90% of the initialvalues.

Example 6

Using the tester 1 against the medium of Example 5, in 32-times velocityrecording, recording method CD1-2 was applied, and this is designated as“recording method CD1-2b”. “Recording method CD1-2b” is a practicalusage wherein the number of independent parameters in the recordingpulse division method (III-A) is further limited.

Recording Method CD1-2b

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m).

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)40 =2.4, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m),

β_(m)′=β_(m)+Δ_(m)′.

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, β₁=1.06, α_(i)=α_(i)′=αc=0.94 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.06, Δ_(m−1)=0.32,α_(m)=0.94, β_(m)=0.44, and Δ_(m)′=0, and they are constant when m is atleast 3. As Δ_(m), Δ_(m)=0.44 was used for m=2, 3 and Δ_(m2)=0.5 wasused for m=4, 5.

However, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in the case where m=2(n=4, 5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′),α₃(α_(m)), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3,respectively.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.81, α₁′=1.94 andβ₁′=0.25.

Then, in the case of 24-times velocity recording, the following“Recording method CD2-2b” was used as a specific example of recordingmethod CD2-2. “Recording method CD2-2b” is a practical usage wherein thenumber of independent parameters in the recording pulse division method(VI) is further limited.

Recording Method CD2-2b

With respect to an even number mark length nT=2mT in the case where m isat least 2, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1) +α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 2, at the time of recording the mark,the mark was divided into m sections, α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β_(i−1)′+α₁′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.8, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m),

β_(m)′m′=β_(m)+Δ_(m)′

Here, T_(d1)=T_(d1)′=1.3, α₁=α₁′=0.7, α_(i)=α₁′=αc=0.7 (αc is constantwith respect to i when i=2 to m−1), β_(m−1)=1.3, Δ_(m−1)=0.4, Δ_(m)=0.4,Δ_(mm)=0.8, α_(m)=0.7, and β_(m)′=0.7, and Δ_(m)′=0, and they areconstant when m is at least 2.

However, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in the case wherem=2(n=4, 5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′),α₃(α₃), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3,respectively.

With respect to 3T mark, T_(d1)′=1.3, α₁′=1.3 and β₁′=1.

Further, in the case of 10-times velocity recording, the following“Recording method CD2-2c” was used as a specific example of recordingmethod CD2-2. “Recording method CD2-2c” is a practical usage wherein thenumber of independent parameters in the recording pulse division method(VI) is further limited.

Recording Method CD2-2c

With respect to an even number mark length nT=2mT in the case where m isat least 2, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 2, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁ ′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1)

β_(m−1)′+α_(m)′=2.6, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m)

β_(m)=α_(m)+Δ_(m)′.

Here, T_(d1)=T_(d1)′=1.7, α₁=α₁′=0.3, α_(i)=α_(i)′=αc=0.3 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.7, Δ_(m−1)=0.3,Δ_(m)=0.3, Δ_(m)=0.6, α_(m)=0.3, and β_(m)=1.2, and Δ_(m)′=0.35, theyare constant when m is at least 2.

However, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in the case where m=2(n=4, 5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′),α₃(α_(m)′), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case wherem=3, respectively.

With respect to 3T mark, T_(d1)′=1.8, α₁′=0.6 and β₁=1.8.

Further, T_(d1), α_(i), β_(i), etc. in each recording method aresummarized in Table 6.

In Table 6, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 6, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, in the recordingpulse division method (III-A), T_(d1)+α_(i)=T_(d1)′+α₁′=2,β₁+α₂=β_(m−1)+α_(m)=2 and α₁=α_(m)=αc were set to be constantirrespective of m.

Therefore, although 10 parameters are presented in Table 6 includingT_(d1), β₁, β_(m−1), β_(m) and α_(m), independent parameters are 6 i.e.α₁, αc, Δ_(m−1), Δ_(m1), Δ_(m2) and Δ_(m)′. However, it is only in thecase of Recording method CD1-2a (32-times velocity) that Δ_(m2) andΔ_(m1) take different values, and Δ_(m1)=0.44 was used when m=2, 3, andΔ_(m2)=0.5 was used when m=4, 5.

Further, when n=4, β₁=β_(m−1) =βc, α ₂=α_(m)=αc and β₂=β_(m). When n=5,β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), and β₂′=β_(m)′. TABLE 6 Recording methodT_(d1) α₁ β₁ αc β_(m−1) Δ_(m−1) α_(m) Δ_(m1) Δ_(m2) β_(m) Δ_(m)′ CD1-2bn = 3 0.81 1.94 0.25 n = 4˜11 1 1 1.06 0.94 1.06 0.32 0.94 0.44 0.5 0.440 CD2-2b n = 3 1.3 1.3 1 n = 4˜11 1.3 0.7 1.3 0.7 1.3 0.4 0.7 0.4 0.40.7 0 CD2-2c n = 3 1.8 0.6 1.8 n = 4˜11 1.7 0.3 1.7 0.3 1.7 0.3 0.3 0.30.3 1.2 0.35

The results of evaluation of overwriting characteristics are shown inFIGS. 32, 33 and 34 in the cases of “Recording method CD1-2b” at32-times velocity, “Recording method CD2-2b” at 24-times velocity and“Recording method CD2-2c” at 10-times velocity. Pe/Pw i.e. the ratio oferasing power Pe to writing power Pw was set to be constant at 0.30 in“Recording method CD1-2b”, 0.33 in “Recording method CD2-2b” and 0.30 in“Recording method CD2-2c”. Pw was changed every 1 mW from 20 mW to about30 mW. Bias power Pb was constant at 0.8 mW.

In the respective Figs., (a) to (f) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁, (d)R_(top), (e) 3T mark length and (f) 3T space length, respectively.

The optimum writing power where the jitter becomes minimum, was from 27to 30 mW in “Recording method CD1-2b” at 32-times velocity, from 25 to30 mW in “Recording method CD2-2b” at 24-times velocity and in thevicinity of from 25 to 30 mW in “Recording method CD2-2c” at 10-timesvelocity, and the overwriting characteristics were evaluated by thevalues at such a power.

The horizontal lines in (a) and (b) in FIGS. 32, 33 and 34 indicate thestandardized upper limit value of jitter=35 (nsec) during retrieving at1-time velocity, and in the vicinity of the optimum Pw, good jittervalues of less than 35 nsec were obtained. Further, the jitters of othermark lengths and space lengths were also less than 35 nsec.

From (c) and (d) in FIGS. 32, 33 and 34, it is evident that in eitherrecording method, the modulation m₁₁, was from 60% to 80% (from 0.6 to0.8), and R_(top) was from 15 to 25%.

In (e) and (f) in FIGS. 32, 33 and 34, the horizontal solid linesindicate 3T mark length=3T space length=231×3 (nsec) during retrievingat 1-time velocity. Further, the horizontal dotted lines indicate 231nsec ×3−40 nsec and 231 nsec×3+40 nsec. With respect to mark lengths andspace lengths, a deviation of about ±20% from the reference clock periodT is usually allowable, and accordingly, a deviation within ±30 to 40nsec is allowable. From the Figs., it is evident that at least in thevicinity of the optimum Pw, there is no substantial deviation of themark lengths and space lengths, and deviations, if any, are within theallowable range. Likewise, in the vicinity of the optimum Pw, also withrespect to the mark lengths and space lengths of from 4T to 11T, desiredmark lengths and space lengths were obtained within a range of thereference clock period T±10%. As the asymmetry value, a value within±10% was obtained.

If the recording medium and the recording method of the this Example areemployed, good recording characteristics will be obtained at leastwithin a range of from 32-times velocity to 10-times velocity, and theretrieving signals will be of a quality retrievable by conventional CDdrives.

Now, the results of evaluation of overwriting durability will bedescribed in cases wherein “Recording method CD1-2b” at 32-timesvelocity, “Recording method CD2-2b” at 24-times velocity, and “Recordingmethod CD2-2c” at 10-times velocity were used. The overwriting cycledependency when repeated overwriting was carried out at Pw/Pe=30 mW/9mW, 28 mW/9.2 mw and 27 mW/8.1 mW, is shown in FIGS. 35, 36 and 37,respectively. In the respective Figs., (a) shows 3T mark length jitter,and (b) shows 3T space length jitter.

At any linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW is sufficiently satisfied.

Further, disks recorded at 32-times velocity by “Recording methodCD1-2b” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was lower than 35 nsec in retrieving at1-time velocity, and the reflectivity R_(top) and the modulation m₁₁also did not substantially decrease and maintained at least 90% of theinitial values.

Example 7

Then, using the tester 1 against the medium of Example 3, overwritingwas carried out at linear velocities of from 8-times velocity to24-times velocity by means of the recording pulse division method(CDE-VI-1), as shown in Table 7. The recording pulse division method(CD-VI-1) is an example wherein the recording pulse division method(VI-B) is applied.

Specifically, overwriting was carried out at 8, 12, 16, 20 and 24-timesvelocities.

In Table 7, the recording pulse division method was presented as dividedinto a case where n=3 and a case where n is from 4 to 11. When n is 3,three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, and in Table 7,they are presented in the columns for T_(d1), αc and β_(m),respectively. When n is from 4 to 11, T_(d1)′, α_(i)=αc (i=1 to m) andα_(i)′=αc (i=1 to m−1) are set to be constant irrespective of n, wherebyT+α₁=T_(d1)′+α_(i)′=2, β_(i−1)+α_(i)=2 (i=2 to m), and β_(i−1)′+α_(i)′=2(i=2 to m−1). Accordingly, β_(i)=2−αc (i=1 to m−1), and β_(i)=2−αc (i=1to m−2). Further, β_(m−1)′=β_(m−1)+Δ_(m−1)βc+Δ_(m−1),α₁′=α_(m)+Δ_(m)=αc+Δ_(m), and β_(m)′=β_(m)+Δ_(m)′, where Δ_(m−1), Δ_(m)and Δ_(m)′ are set to be constant irrespective of m. With respect to n=4to 11 (m being at least 2), independent parameters are αc, Δ_(m−1),Δ_(m), β_(m) and Δ_(m)′.

Further, when m=2 (n=4,5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are setto be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) andβ_(m)′ in the case where m is 3, respectively. Accordingly, when n=4,β₂=β_(m). When n=5, β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), β₂=β_(m)+Δ_(m)′.

As Pw, Pw₀ was selected as the writing power with which the jitter valuewould be minimum, whereby repeated overwriting was carried out. Further,the Pe/Pw ratio at that time is also shown in Table 7. Pb was set to beconstant at 0.8 mW, and Pe/Pw was set to be constant at 0.30. TABLE 7-times Pe/ velocity n T_(d1) αc Δ_(m−1) Δ_(m) β_(m) Δ_(m)′ Pw₀ Pw 8 31.65 0.50 1.9 24 0.30 4˜11 1.65 0.35 0.25 0.15 1 0.55 24 0.30 12 3 1.450.9 1.6 25 0.30 4˜11 1.5 0.5 0.3 0.3 0.75 0.45 25 0.30 16 3 1.3 1.051.35 26 0.30 4˜11 1.35 0.65 0.35 0.25 0.5 0.4 26 0.30 20 3 1.1 1.2 0.927 0.30 4˜11 1.15 0.85 0.35 0.15 0.4 0.15 27 0.30 24 3 0.9 1.6 0.55 260.30 4˜11 1 1 0.4 0.45 0.3 0 26 0.30

FIG. 38 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 12, 16, 20 and 24-times velocities.

The symbol “×” in FIGS. 38(a) to (d) means “-times velocity”. Forexample, “8×” means 8-times velocity. The same applies in the followingExamples.

At each linear velocity, good jitter values of less than 35 nsec wereobtained with respect to mark lengths and space lengths in retrieving at1-time velocity within a range of about Pw₀±1 mW. Likewise, with respectto all mark length and space length jitters, good jitters of less than35 nsec were obtained.

Further, at each linear velocity, the modulation m₁₁ was from 60% to 80%(0.6 to 0.8), R_(top) was from 15 to 25%, and the asymmetry value was avalue within ±10%. In the vicinity of Pw₀, the desired mark lengths andspace lengths were obtained within a range of the reference clock periodT±10% with respect to any of mark lengths and space lengths of from 3Tto 11T. At each linear 2C velocity, the maximum value of Pw₀ was 27 mW,and the minimum value was 24 mW, and the ratio of the minimum value tothe maximum value was 0.89.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 39when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 7. In FIG. 39, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

In summarizing the foregoing, when the recording medium and therecording pulse division method (CD-VI-1) of the present invention areapplied, good characteristics can be obtained by the recording pulsedivision method having a small number of parameters made variable,within a wide range of from 8 to 24-times velocities.

Example 8

Then, using the tester 1 against the medium of Example 5, overwritingwas carried out at linear velocities of from 8-times velocity to32-times velocity by means of the recording pulse division method(CDE-VI-2), as shown in Table 8. The recording pulse division method(CD-VI-2) is an example wherein the recording pulse division method(VI-B) is applied.

Specifically, overwriting was carried out at 8, 16, 24, 28 and 32-timesvelocities.

In Table 8, the recording pulse division method was presented as dividedinto a case where n=3 and a case where n is from 4 to 11. When n is 3,three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, and in Table 8,they are presented in the columns for T_(d1), αc and β_(m),respectively. When n is from 4 to 11, T_(d1), α_(i)=αc (i=1 to m) andα_(i)′=αc (i=1 to m−1) are set to be constant irrespective of n, wherebyT_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2 to m), andβ_(i−1)′+α_(i)′=2 (i=2 to m−1). Accordingly, β_(i)=2−αc (i=to m−1), andβ_(i)′=2−αc (i=1 to m−2). Further, β_(m−1)′=β_(m−1)+Δ_(m−1)=βc +Δ_(m−1),α_(m)′=α_(m)+Δ_(m)=αc+Δ_(m), and β_(m)′=β_(m)+Δ_(m)′, where Δ_(m−1),Δ_(m) and Δ_(m)′ are set to be constant irrespective of m. With respectto n=4 to 11 (m being at least 2), independent parameters are αc,Δ_(m−1), Δ_(m), β_(m) and Δ_(m)′.

Further, when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ areset to be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) andβ_(m)′ in the case where m is 3, respectively. Accordingly, when n=4,β₂=β_(m). When n=5, β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), β₂′=β_(m)=Δ_(m)′.

As Pw, Pw₀ was selected as the writing power with which the jitter valuewould be minimum, whereby repeated overwriting was carried out. Further,the Pe/Pw ratio at that time is also shown in Table 8. Pb was set to beconstant at 0.8 mW, and Pe/Pw was set to be constant at 0.30. TABLE 8-times Pe/ velocity n T_(d1) αc Δ_(m−1) Δ_(m) β_(m) Δ_(m)′ Pw₀ Pw 8 31.9 0.4 2 0.30 4˜11 1.75 0.25 0.2 0.05 1.3 0.65 26 0.30 16 3 1.55 0.91.5 0.30 4˜11 1.5 0.5 0.2 0.2 0.8 0.65 27 0.30 24 3 1.25 1 0.9 0.30 4˜111.25 0.35 0.25 0.25 0.65 0.3 28 0.30 28 3 1.15 1.75 0.65 0.30 4˜11 1.150.85 0.25 0.45 0.55 0.05 29 0.30 32 3 1.88 1.94 0.24 0.30 4˜11 0 1 0.380.38 0.4 0 29 0.30

FIG. 40 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 16, 24, 28 and 32-times velocities.

At each linear velocity, good jitter values of less than 35 nsec wereobtained with respect to mark lengths and space lengths in retrieving at1-time velocity within a range of about Pw₀±1 mW. Likewise, with respectto all mark length and space length jitters, good jitters of less than35 nsec were obtained.

Further, at each linear velocity, the modulation m₁₁, was from 60% to80% (0.6 to 0.8), R_(top) was from 15 to 25%, and the asymmetry valuewas a value within ±10%. In the vicinity of Pw₀, the desired marklengths and space lengths were obtained within a range of about ±10%with respect to any of mark lengths and space lengths of from 3T to 11T.At each linear velocity, the maximum value of Pw₀ was 29 mW in the caseof 32-times velocity, and the minimum value was 26 mW in the case of8-times velocity, and the ratio of the minimum value to the maximumvalue was 1.12.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 41when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 8. In FIG. 41, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

In summarizing the foregoing, when the recording medium and therecording pulse division method (CD-VI-2) of the present invention areapplied, good characteristics can be obtained by the recording pulsedivision method having a small number of parameters made variable,within a wide range of from 8 to 32-times velocities.

Here, as parameters particularly important to obtain low jitters, thelinear velocity dependency of αc, β_(m), Δ_(m−1), Δ_(m) and Δ_(m)′ inthe case where n is at least 4, is shown in FIG. 42, and the linearvelocity dependency of T_(d1)′, α₁′ and β₁′ in the case where n=3, isshown in FIG. 43. FIG. 42 is one wherein αc, β_(m), Δ_(m−1)Δ_(m) andΔ_(m)′ where n=4 to 11 in Table 8 were plotted against the respectivelinear velocities. On the other hand, FIG. 43 is one wherein T_(d1)′,α₁′ and β₁′ where n=3 in Table 8 were plotted against the respectivelinear velocities. As is apparent from FIGS. 42 and 43, although thereis some fluctuation, each parameter changes substantially monotonouslydepending upon the linear velocity, and αc, Δ_(m−1), Δ_(m) and α₁′ takesmaller values as the linear velocity is lower, while β_(m), Δ_(m),T_(d1)′ and β₁′ take larger values as the linear velocity is lower.

And, it is evident that at least with respect to αc, T_(d1)′, α₁′ andβ₁′, values having their parameter values at the maximum and minimumvelocities substantially linearly complemented, may be applied inrecording in a wide range of the linear velocity.

Example 9

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 90 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 18 nm of a recording layer made ofGe₅In₁₈Sb₇₂Te₅(Te_(0.05)In_(0.18)(Ge_(0.06)Sb_(0.94))_(0.77)), 27 nm ofan upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 3 nm of aninterfacial layer made of GeN, 200 nm of a reflective layer made of Agand about 4 μm of an ultraviolet-curable resin layer, were formed inthis order to obtain a rewritable compact disk. Here, the meaning of(ZnS)₈₀(SiO₂)₂₀ indicates that it is a film obtained by high frequencysputtering of a target having 80 mol % of ZnS and 20 mol % of SiO₂mixed. Further, the compositional ratio in Ge₅In₁₈Sb₇₂Te₅ is an atomicratio. The same applies in the following Examples.

The volume resistivity ρ_(v) of this Ag reflective layer was about 24nΩ·m, and the sheet resistivity ps was about 0.12 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 75 μm and a minor axis of about 1.0 μm, in the minor axisdirection at a linear velocity of about 12 m/s. The irradiation powerwas about 1100 mW.

On this disk, by means of the tester 2 with NA=0.50, overwriting of EFMmodulation signal was carried out at 24 and 8-times velocities, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 2 mW from about 26 mW toabout 36 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Each was evaluated by the value afteroverwriting ten times.

In 24-times velocity recording, recording method CD1-2 was applied, andthis is designated as “recording method CD1-2c”. “Recording methodCD1-2c” is a practical method wherein the number of independentparameters in the recording pulse division method (III-A) is furtherlimited.

Recording Method CD1-2c

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.85, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m),

β_(m)′=β_(m)+Δ_(m)′.

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, α_(i)=α₁′=αc=0.9 (αc is constant withrespect to i when i=2 to m−1), β_(m−1)=1.1, Δ_(m−1)=0.35, Δ_(m)=0.5,Δ_(m)=0.85, α_(m)=0.9, and β_(m)=0.4, and Δ_(m)′=0, and they areconstant when m is at least 2.

However, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ in the case where m=2(n=4, 5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′),α₃(α_(m)), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3,respectively. Namely, with respect to 4T mark, α₁=1, β₁=1.1, α₂=0.9 andβ_(m)=0.4, and with respect to 5T mark, α₁=1, β₁′=1.45, α₂′=1.4 andβ_(m)′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.9, α₁′=1.4 andβ₁′=0.85.

On the other hand, in the case of 8-times velocity recording, thefollowing “Recording method CD2-2d” was used as recording method CD2-2.“Recording method CD2-2d” is a practical usage wherein the number ofindependent parameters in the recording pulse division method (VI) isfurther limited.

Recording Method CD2-2d

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+αα₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.4, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m),

β_(m)′=β_(m)+Δ_(m)′.

Here, T_(d1)=T_(d1)′=1.65, α₁=α₁′=0.35, α_(i)=α_(i)′=αc=0.35 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.65, Δ_(m−1)=0.25,Δ_(m)=0.15, Δ_(mm)=0.4, α_(m)=0.35, β_(m−1)=1.0, and Δ_(m)′=0.55, andthey are constant when m is at least 2.

However, α₁, α₁′, β₁, β₁′, α₂′, β₂ and β₂′ in the case where m=2 (n=4,5) were set to be equal to α₁, α₁′, β₂(β_(m−1)), β₂′(β_(m−1)′), α₃(α_(m)), α₃′(α_(m)′), β₃(β_(m)) and β₃′(β_(m)′) in the case where m=3,respectively. Namely, with respect to 4T mark, α₁=0.35, β₁=1.65, α₂=0.35and β_(m)=1.0, and with respect to 5T mark, α₁′=0.35, β₁′=1.9, α₂′=0.5and β₂′=1.55.

With respect to 3T mark, T_(d1)′=1.65, α₁′=0.5 and β₁′=1.9.

Further, T_(d1), α_(i), β_(i), etc. in each recording method aresummarized in Table 9.

In Table 9, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁α₁′ and β₁′ are required,and in Table 9, they are presented in the columns for T_(d1), α₁ andβ_(m), respectively. In the case where n is from 4 to 11, in therecording pulse division method (III-A), T_(d1)+α₁=T_(d1)′+α₁′=2,β₁+α₂=β_(m−1)+α_(m)=2, α₁=α_(m)=αc and Δ_(m) were set to be constantirrespective of m. Therefore, although 10 parameters are presented inTable 9 including T_(d1), β₁, β_(m−1), β_(m) and α_(m), independentparameters are 5 i.e. α₁, αc, Δ_(m−1), Δ_(m) and Δ_(m)′. Further, whenn=4, β₁=β_(m−1)=βc, α₂=α_(m) =αc and β ₂=β_(m). When n=5,β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), and β₂′=β_(m)′. TABLE 9 Recording methodTd1 α1 β1 αc βm − 1 Δm − 1 αm Δm βm Δm′ CD1-2c n = 3 0.9 1.4 0.85 n =4˜11 1 1 1.1 0.9 1.1 0.35 0.9 0.5 0.4 0 CD2-2d n = 3 1.65 0.5 1 n = 4˜111.65 0.35 1.65 0.35 1.65 0.25 0.35 0.15 0 0.55

The results of evaluation of overwriting characteristics in the cases of“Recording method CD1-2c” at 24-times velocity and “Recording methodCD2-2d” at 8-times velocity, are shown in FIG. 44. Pe/Pw i.e. the ratioof erasing power Pe to writing power Pw was set to be constant at 0.27in “Recording method CD1-2c” at 24-times velocity and at 0.27 in“Recording method CD2-2d at 8-times velocity”. In “Recording methodCD1-2c”, Pw was changed every 2 mW from about 26 mW to about 38 mW. In“Recording method CD2-2d”, Pw was changed every 2 mW from about 26 mW toabout 36 mW. Bias power Pb was constant at 0.8 mW.

In the respective Figs., (a) to (d) show the Pw dependency of (a) 3Tmark length jitter, (b) 3T space length jitter, (c) modulation m₁₁, and(d) R_(top), respectively.

The optimum writing power was in the vicinity of from 28 to 32 mW in“Recording method CD1-2c” at 24-times velocity and in the vicinity offrom 28 to 32 mW in “Recording method CD2-2d” at 8-times velocity, andthe overwriting characteristics were evaluated by the values at such apower.

The horizontal lines in FIGS. 44(a) and (b) indicate the standardizedupper limit value of jitter=35 (nsec) during retrieving at 1-timevelocity. Good jitter values of less than 35 nsec were obtained ateither linear velocity.

From FIGS. 44(c) and (d), it is evident that in either recording method,the modulation m₁₁ was from 60% to 80% (from 0.6 to 0.8), and R_(top)was from 15 to 25%, at either linear velocity.

Further, in the vicinity of the optimum writing power, with respect tothe mark lengths and space lengths of from 3T to 11T, desired marklengths and space lengths were obtained within a range of the referenceclock period T±10%. As the asymmetry value, a value within ±10% wasobtained.

In summarizing the foregoing, good recording characteristics wereobtained at 8 and 24-times velocities, and the retrieving signals wereof a quality retrievable by conventional CD drives. Further, by makingthe recording pulse division method variable as in the presentinvention, good characteristics will be obtained also at linearvelocities between them.

Now, the results of evaluation of overwriting durability will bedescribed in cases wherein “Recording method CD1-2c” at 24-timesvelocity and “Recording method CD2-2d” at 8-times velocity were used.The overwriting cycle dependency when repeated overwriting was carriedout at Pw/Pe=30 mW/8 mW, is shown in FIGS. 45. In the respective Figs.,(a) shows 3T mark length jitter, and (b) shows 3T space length jitter.In FIGS. 45, for the purpose of showing the number of cycles of repeatedoverwriting on a logarithmic graph, the first recording is representedby first overwriting, and when overwriting was carried out nine timesthereon, is represented by 10th overwriting. Also in the followingExamples, the number of cycles of repeated overwriting is shown in thesame manner on a logarithmic axis.

At each linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW is sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. The3T/11T overwriting erase ratio was measured at 8-times velocity by using3T and 11T pulses of “Recording method CD2-2d”, and at 24-times velocityby using 3T and 11T pulses of “Recording method CD1-2c”. The 3T/11Toverwriting erase ratios at 8-times velocity and 24-times velocity wereat least 25 dB, respectively and thus sufficient erase ratios wereobtained at the respective linear velocities.

Further, disks recorded at 24-times velocity by “Recording methodCD1-2c” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to have changed by about 2nsec, but still was lower than 35 nsec in retrieving at 1-time velocity,and the reflectivity R_(top) and the modulation m₁₁ also did notsubstantially decrease and maintained at least 90% of the initialvalues.

Example 10

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 90 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 18 nm of a recording layer made ofGe₃In₁₈Sb₇₄Te₅(Te_(0.05)In_(0.18)(Ge_(0.04)Sb_(0.96))_(0.77)), 27 nm ofan upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 3 nm of aninterfacial layer made of GeN, 200 nm of a reflective layer made of Agand about 4 μm of an ultraviolet-curable resin layer, were formed inthis order to obtain a rewritable compact disk. Here, the meaning of(ZnS)₈₀(SiO₂)₂₀ indicates that it is a film obtained by high frequencysputtering of a target having 80 mol % of ZnS and 20 mol % of SiO₂mixed. Further, the compositional ratio in Ge₃In₁₈Sb₇₄Te₅ is anatomicity ratio. The same applies in the following Examples.

The volume resistivity ρ_(v) of this Ag reflective layer was about 24nΩ·m, and the sheet resistivity ρ_(s) was about 0.12 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 75 μm and a minor axis of about 1.0 μm, in the minor axisdirection at a linear velocity of about 12 m/s. The Irradiation powerwas about 950 mW.

On this disk, by means of the tester 2 with NA=0.50, overwriting of EFMmodified signal was carried out at 8, 16, 24 and 32-times velocities bymeans of the recording method as shown in Table 10, and thecharacteristics were evaluated.

The recording pulse division method at 32-times velocity is an exampleof “Recording method 1-2” and will be referred to as “Recording methodCD1-2d”. Further, the recording pulse division method at 8, 16 and24-times velocity is an example of “Recording method 2-2” and will bereferred to as “Recording method CD2-2e”.

In Table 10, the recording pulse division method was presented asdivided into a case where n=3 and a case where n is from 4 to 11. When nis 3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, and inTable 10, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. When n is from 4 to 11, T_(d1), α₁, α₁′, α_(i)=αc (i=2 tom) and α_(i)=αc (i=2 to m−1) are set to be constant irrespective of n,whereby T_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2 to m), andβ_(i−1)′+α_(i)′=2 (i=2 to m−1). Accordingly, β_(i)=2−αc (i=2 to m−1),and β_(i)′=2−αc (i=2 to m−2). Further,β_(m−1)′=Δ_(m−1)+Δ_(m−1)=βc+Δ_(m−1), α_(m)′=α_(m)+Δ_(m)=αc+Δ_(m), andΔ_(m)′=β_(m)+Δ_(m)′, where Δ_(m−1), Δ_(m) and Δ_(m)′ are set to beconstant irrespective of m. With respect to n=4 to 11 (m being at least2), independent parameters are α₁, αc, Δ_(m−1), Δ_(m), Δ_(m) and Δ_(m)′.

Further, when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂′, α₂′, β₂ and β₂′ areset to be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) andβ_(m)′ in the case where m is 3, respectively. Accordingly, when n=4,β₂=Δ_(m). When n=5, β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), β₂′=β_(m)+Δ_(m)′.

Each recording method in Table 10 is also an example of the recordingpulse division method (VI-A) of the present invention, and is furtherequivalent to the recording pulse division method (VI-B) except thatα₁≠αc at 32-times velocity.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 29 mW toabout 40 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Each was evaluated by the value afteroverwriting ten times. Bias power Pb was set to have a constant value ofsubstantially 0 mW, and Pe/Pw was set to be constant at 0.27. Pw₀ as awriting power with which the jitter value would be minimum, is show inTable 10. TABLE 10 Recording -times method velocity Td1 α1 αc Δm − 1 Δmβm Δm′ Pw0 Pe/Pw CD2-2e 8 3 1.90 0.40 — — — 2.20 — 35 0.27 4˜11 1.750.25 0.25 0.20 0.05 1.50 0.65 16 3 1.50 0.90 — — — 1.60 — 35 0.27 4˜111.50 0.50 0.50 0.20 0.20 1.00 0.45 24 3 1.25 1.20 — — — 1.10 — 35 0.274˜11 1.25 0.75 0.75 0.30 0.45 0.80 0.00 CD1-2d 32 3 0.94 1.63 — — — 0.25— 35 0.27 4˜11 1.00 1.00 0.94 0.19 0.44 0.38 0.00

FIG. 46 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 16, 24 and 32-times velocities.

At each linear velocity, good jitter values of less than 35 nsec wereobtained with respect to mark lengths and space lengths in retrieving at1-time velocity within a range of about Pw₀±1 mW. Likewise, with respectto all mark length and space length jitters, good jitters of less than35 nsec were obtained.

Further, at each linear velocity, at least within a range of about Pw₀±1mW, the modulation m₁₁ was from 60% to 80% (0.6 to 0.8), R_(top) wasfrom 15 to 25%, and the asymmetry value was a value within ±10%. In thevicinity of Pw₀, the desired mark lengths and space lengths wereobtained within a range of the reference clock period T±20% with respectto any of mark lengths and space lengths of from 3T to 11T.

In summarizing the foregoing, when the recording medium of the presentinvention and the recording pulse division method (VI-A) of the presentinvention are applied, good characteristics can be obtained by therecording pulse division method having a small number of parameters madevariable, within a wide range of from 8 to 32-times velocities, and theretrieved signals are of a quality retrievable by conventional CDdrives. Further, even between these linear velocities, goodcharacteristics can be obtained by making the recording pulse divisionmethod variable as in the present invention.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 47when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 10. In FIG. 47, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

At each linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW is sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. The3T/11T overwriting erase ratio measured by using 3T and 11T pulses ofthe recording pulse division methods in Table 10 were at least 25 dB,respectively, at 8-times velocity and 32-times velocity, and thussufficient erase ratios were obtained at the respective linearvelocities.

Further, disks recorded at 32-times velocity by “Recording methodCD1-2d” in Table 10 were subjected to an accelerated test at 105° C.,whereby even upon expiration of 3 hours, no substantial deterioration ofthe recorded signals was observed. The jitter was found to have changedby about 2 nsec, but still was lower than 35 nsec in retrieving at1-time velocity, and the reflectivity R_(top) showed a decrease of alittle more than 10% of the initial value, but the modulation m₁₁ didnot substantially decrease and maintained at least 90% of the initialvalues.

Example 11

On the disk of Example 9, by means of the tester 2 with NA=0.50,overwriting of EFM modulation signal was carried out at 24-timesvelocity by the following three types of recording methods, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant at 0.27, Pw was changed every 1 mW from about26 mW to about 36 mW, whereby the overwriting characteristics at therespective writing powers were evaluated. Each was evaluated by thevalue after overwriting ten times. Bias power Pb was set to have aconstant value of approx. zero.

Recording Method CD1-2e

This recording method is a practical usage wherein the number ofindependent parameters in the recording pulse division method (III-A) isfurther limited.

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.85, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m),

β_(m)′=β_(m)+Δ_(m)′.

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, α_(i)=α₁′=αc=0.9 (αc is constant withrespect to i when i=2 to m−1), β_(m−1)=1.1, Δ_(m−1)=0.35, Δ_(m)=0.5,Δ_(mm)=0.85, α_(m)=0.9, β_(m)=0.4, and Δ_(m)′=0 and they are constantwhen m is at least 2.

However, β₁, α₂, β₂, β₁′, α₂′ and β₂′ in the case where m=2 are deemedto be β_(m−1), α_(m), β_(m), β_(m−1)′, α_(m)′ and β_(m)′ in the casewhere m is at least 3. Namely, with respect to 4T mark, β₁=1.1, α₂=0.9and β_(m)=0.4, and with respect to 5T mark, β₁′=1.45, α₂′=1.4 andβ_(m)′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=1.0 , α₁′=1.4 andβ₁′=0.85.

Further, T_(d1), α_(i), β_(i), etc. in each recording method aresummarized in Table 11.

In Table 11, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 11, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, in the recordingpulse division method (III-A), T_(d1)+α₁=T_(d1)′+α₁′=2, β₁+α₂=0β_(m−1)+α_(m)=2, α₁=α_(m)=αc and Δ_(m) were set to be constantirrespective of m. Therefore, although 10 parameters are presented inTable 11 including T_(d1), β₁, β_(m−1), β_(m) and α_(m), independentparameters are 5 i.e. α₁, αc, Δ_(m−1), Δ_(m) and Δ_(m)′. Further, whenn=4, β₁=β_(m−1)=βc, α₂=α_(m)=αc and β₂=β_(m). When n=5, β₁′=βc +Δ_(m−1),α₂=αc+Δ_(m), and β₂′=β_(m)′. TABLE 11 Recording method Td1 α1 β1 αc βm −1 Δm − 1 αm Δm βm Δm′ CD1-2e n = 3 1 1.4 0.85 n = 4˜11 1 1 1.1 0.9 1.10.35 0.9 0.5 0.4 0Comparative Recording Pulse Division Method I

This recording pulse division method resembles the recording pulsedivision method (II-A) of the present invention, but is different fromthe recording method of the present invention in that α_(m)=α_(m)′ i.e.Δ_(m)=0. Specifically:

Comparative Recording Method CD1

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β₁′+α₂=2.45, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.45, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m),

β_(m)=β_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, β₁=1.1, Δ₁=0.45, α_(i)=α_(i)′=αc=0.9(αc is constant with respect to i when i=2 to m−1), β_(m−1)=1.1,Δ_(m−1)=0.45, Δ_(m)=0, Δ_(mm)=0.45, α_(m)=0.9, β_(m)=β_(m)′=0.4, andΔ_(m)′=0, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1, α₁=1, β₁=1.1,α₂=α_(m)=0.9 and β_(m)=0.4,

with respect to 5T mark, T_(d1)′=1, α₁′=1, β₁′=1.45, α₂′=α_(m)′=0.9 andβ_(m)′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=1, α₁′=1.4 and β₁′=0.85.

Further, T_(d1)′, α_(i), β_(i), etc. in “Comparative recording methodCD1” are summarized in Table 12. In the case where m is at least 3, tenparameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m)andβ_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, in the recordingpulse division method (II), are presented. However, (T_(d1)′, α₁′ andβ₁′) in the case where n=3 are presented in the columns for T_(d1), α₁and β₁. (T_(d1), α₁, β₁, α₂ and β₂) in the case where n=4 and (T_(d1)′,α₁′, β₁′, α₂′ and β₂′) in the case where n=5 are presented in thecolumns for T_(d1), α₁, β₁, α_(m) and β_(m). Here, this method isdifferent from of the present invention in that Δ_(m)=0. TABLE 12Recording method Td1 α1 β1 Δ1 αc βm − 1 Δm − 1 αm Δm βm Comparative m ≧3 1 1 1.1 0.45 0.9 1.1 0.45 0.9 0 0.4 recording n = 5 1 1 1.45 1.4 0.4method n = 4 1 1 1.1 0.9 0.4 CD1 n = 3 1 1.4 0.85Comparative Recording Pulse Division Method II

This recording pulse division method is different from the recordingpulse division method (II-A) of the present invention in that it isdesigned to impart the mark length difference of 1T between an evennumber length mark and an odd number length mark for the same m when mis at least 3, solely by Δ_(m) (solely by α_(m)≠α_(m)′). Specifically:

Comparative Recording Method CD2

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1)

β_(m−1)′+α_(m)′=2.6, provided that β_(m−1′=β) _(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m),

β_(m)′=β_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1 , β₁=1.1, α_(i)=α_(i)′=αc=0.9 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.1, Δ_(m−1)=0,Δ_(m)=0.6, Δ_(mm)=0.6, α_(m)=0.9, β_(m)=β_(m)′=0.4, and Δ_(m)′=0, andthey are constant when m is at least 3.

However, β₁, α₂, β₂, β₁′, α₂′ and β₂′ in the case where m=2 are deemedto be β_(m−1), α_(m), β_(m), β_(m−1)′, α_(m)′ and β_(m)′in the casewhere m is at least 3. Namely, with respect to 4T mark, β₁=1.1, α₂=0.9and β_(m)=0.4, and with respect to 5T mark, β₁=1.1, α₂′=1.5 andβ_(m)′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=1.0, α₂′=1.4 andβ₁′=0.85.

Further, T_(d1)′, α_(i), β_(i), etc. in the recording method aresummarized in Table 13.

In Table 13, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 13, they are presented in the columns for T_(d1), α₁ and β_(m),respectively.

Further, when n=4, β₁=β_(m−1)=βc, α₂=α_(m)=αc and β₂=Δ_(m). When n=5,β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m), and β₂′=β_(m)′. TABLE 13 Recording methodTdI α1 β1 αc βm − 1 Δm − 1 αm Δm βm Δm′ Comparative n = 3 1 1.4 0.85recording n = 4˜11 1 1 1.1 0.9 1.1 0 0.9 0.6 0.4 0method CD2

The results of evaluation of overwriting characteristics in the cases of“Recording method CD1-2e”, “Comparative recording method CD1” and“Comparative recording method CD2”, are shown in FIGS. 48. In FIGS. 48,(a) to (d) show the Pw dependency of (a) 3T mark length jitter, (b) 3Tspace length jitter, (c) modulation m₁₁ and (d) R_(top), respectively.

The optimum writing power was in the vicinity of from 28 to 33 mW in“Recording method CD1-2e”, in the vicinity of from 29 to 33 mW in“Comparative recording method CD1”, and in the vicinity of from 29 to 34mW in “Comparative recording method CD2”, and the overwritingcharacteristics were evaluated by the values at such a power.

The horizontal lines in FIGS. 48(a) and (b) indicate the standardizedupper limit value of jitter=35 (nsec) during retrieving at 3-timevelocity. In each case, good jitter values of less than 35 nsec wereobtained.

From FIGS. 48(c) and (d), it is evident that in each case, themodulation m₁₁ was from 60% to 80% (from 0.6 to 0.8), and R_(top) wasfrom 15 to 25%.

Further, in the vicinity of the optimum writing power, in each case,with respect to the mark lengths and space lengths of from 3T to 11T,desired mark lengths and space lengths were obtained within a range ofthe reference clock period T±20%. As the asymmetry value, a value within±10% was obtained.

However, the 3T space jitter values by “Comparative recording methodCD1” and by “Comparative recording method CD2” were slightly higher thanthe 3T space jitter values by “Recording method CD1-2e”.

Now, the results of evaluation of overwriting durability are shown inFIGS. 49 in cases wherein “Recording method CD1-2e”, “Comparativerecording method CD1” and “Comparative recording method CD2” were used.In the evaluation of the repeated overwriting characteristics, Pw/Pe in“Recording method CD1-2e” was set to be Pw/Pe=30 mW/8 mW; Pw/Pe in“Comparative recording method CD1” was set to be Pw/Pe=31 mW/8.4 mW; andPw/Pe in “Comparative recording method CD2” was set to be Pw/Pe=31mW/8.4 mW.

In FIGS. 49, (a) shows 3T mark length jitter, and (b) shows 3T spacelength jitter. In FIGS. 49, for the purpose of showing the repeatedoverwriting cycle number in a logarithmic graph, the first recording isrepresented by the first overwriting, and when overwriting was carriedout 9 times thereon, is represented by the 10th overwriting.

FIGS. 49(a) and (b) show such results that when recording was carriedout by “Recording method CD1-2e”, the jitter value was less than 35 nseceven after overwriting 1000 times, while when recording was carried outby “Comparative recording method CD1” and by “Comparative recordingmethod CD2”, the space length jitter values after overwriting 1000 timesexceeded 35 ns.

Example 12

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 95 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 15 nm of a recording layer made ofGe₁₆Sb₆₄Sn₂₀(Sn_(0.2)(Ge_(0.2)Sb_(0.8))_(0.8)), 30 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 4 nm of an interfacial layermade of Ta, 210 nm of a reflective layer made of Ag and about 4 μm of anultraviolet-curable resin layer, were formed in this order to obtain arewritable compact disk. Here, the meaning of (ZnS)₈₀(SiO₂)₂₀ indicatesthat it is a film obtained by high frequency sputtering of a targethaving 80 mol % of ZnS and 20 mol % of SiO₂ mixed. Further, thecompositional ratio in Ge₁₆Sb₆₄Sn₂₀ is an atomic ratio. The same appliesin the following Examples.

The volume resistivity ρ_(v) of this Ag reflective layer was about 27nΩ·m, and the sheet resistivity ρ_(s) was about 0.13 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 75 μm and a minor axis of about 1.0 μm in the minor axisdirection at a linear velocity of about 12 m/s. The irradiation powerwas about 950 mW.

On this disk, by means of the tester 2 with NA=0.50, overwriting of EFMmodulation signal was carried out at 24-times velocity by threerecording methods of Example 10, i.e. “Recording method CD1-2e”,“Comparative recording method CD1” and “Comparative recording methodCD2”, and the characteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 26 mW toabout 40 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Each was evaluated by the value afteroverwriting ten times. Bias power Pb was set to be constant atsubstantially zero.

The results of evaluation of overwriting characteristics are shown inFIGS. 50 in the cases where recording was carried out by the respectiverecording methods i.e. “Recording method CD1-2e”, “Comparative recordingmethod CD1” and “Comparative recording method CD2”.

FIGS. 50(a) to (d) show the Pw dependency of (a) 3T mark length jitter,(b) 3T space length jitter, (c) modulation m₁₁ and (d) R_(top),respectively.

The optimum writing power was in the vicinity of from 29 to 37 mW in“Recording method CD1-2e”, in the vicinity of from 30 to 37 mW in“Comparative recording method CD1” and in the vicinity of from 35 to 37mW in “Comparative recording method CD2”, and the overwritingcharacteristics were evaluated by the values at such a power.

From FIGS. 50(c) and (d), it is evident that in each case, themodulation m₁₁ was from 60% to 80% (from 0.6 to 0.8), and R_(top) wasfrom 15 to 25%.

Further, in the vicinity of the optimum writing power, in each case,with respect to the mark lengths and space lengths of from 3T to 11T,desired mark lengths and space lengths were obtained within a range ofabout ±10%. As the asymmetry value, a value within ±10% was obtained.

As is apparent from FIG. 50(b), 3T space jitters are good at a level ofless than 35 nsec when recording is carried out by “Recording method1-2e”. However, it is apparent that if recording is carried out by“Comparative recording method CD1” and “Comparative recording methodCD2”, 3T space length jitters tend to be high as compared with a casewhere recording is carried out by “Recording method CD1-2e”). Especiallyby “Comparative recording method CD2”, 3T space length jitters were morethan 35 nsec at all Pw.

Now, the results of evaluation of overwriting durability are shown inFIGS. 51 in cases wherein “Recording method CD1-2e” and “Comparativerecording method CD1” were used. In the measurement of overwritingdurability, Pw/Pe was set to be 33 mW/9 mW when recording was carriedout by “Recording method CD1-2e”, and Pw/Pe was set to be 33 mW/9 mWwhen recording was carried out by “Comparative recording method CD1”.Further, no evaluation of overwriting durability was carried out by“Comparative recording method CD2”, since even the initial jittercharacteristics were poor.

In FIG. 51, (a) shows 3T mark length jitter, and (b) shows 3T spacelength jitter. In FIG. 51, for the purpose of showing the repeatedoverwriting cycle number in a logarithmic graph, the first recording isrepresented by the first overwriting, and when overwriting was repeated9 times thereon, is represented by the 10th overwriting. When recordingwas carried out by “Recording method CD1-2e”, the jitter value was lessthan 35 nsec even alter overwriting 1000 times. On the other hand, by“Comparative recording method CD1”, in all overwriting cycle numbers,the space length jitter values were higher than the space length jittervalues in the case where recording was carried out by “Recording methodCD1-2e”.

Also from the foregoing results, the superiority of the “Recordingmethod CD1-2e” as the recording pulse division method (III-A) of thepresent invention is evident.

Further, in “Comparative recording method CD1”, a difference Δ₁ is givenbetween β₁ and β₁′, whereby the design of the recording pulse-generatingcircuit will be complicated, since all of the subsequent recordingpulses will not synchronize with the reference clock, unless Δ₁ is avalue capable of synchronizing with the reference clock period T (forexample, unless Δ₁ is integral multiples (practically 1 or 2-timesperiod) of the reference clock period T, or unless Δ₁ is 1/integralmultiples (practically ½T or ¼) of the reference clock period T).Especially when it is attempted to employ “Comparative recording methodCD1” in P-CAV or CAV system, the recording pulse-generating circuit willbe more complicated.

On the other hand, “Comparative recording method CD2” has a merit inthat the recording pulse-generating circuit can be simplified, since itrequires only to give Δ_(m) between α_(m) and α_(m)′. However, in a casewhere the optical recording medium in this Example is to be used at alow linear velocity at a level of 8-times velocity or 16-times velocity,cooling tends to be inadequate by “Comparative recording method CD2” asit does not control β_(i) and β_(i)′, whereby the difference from therecording method of the present invention such as “Recording methodCD1-2e” will be more distinct. Namely, the quality of record signalsrecorded by “Comparative recording method CD2” at a low linear velocitywill be poorer.

Example 13

On the disk of Example 12, overwriting of EFM modulation signals wascarried out by means of tester 2 having NA=0.50 at linear velocities offrom 8-times velocity to 24-times velocity by the following three typesof recording pulse division methods, and the characteristics wereevaluated. The following three types of recording pulse division methodsare examples wherein the number of parameters variable depending uponthe linear velocity is particularly reduced to facilitate findingoptimum parameters for every linear velocity, among recording pulsedivision methods (VI), (VI-A) and (VI-B) to enable overwriting in a widerange of linear velocities by e.g. CAV or P-CAV.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant at 0.27, Pw was changed, and overwritingcharacteristics were evaluated at the respective writing powers. Eachwas evaluated by the values after overwriting 10 times. Pb was set to beconstant at approx. 0 mW.

Recording Pulse Division Method CD-VI-3

This recording method is an example of the recording pulse divisionmethod (VI-B), but Δ_(m−1)=0, and only Δ_(m) and Δ_(m)′ are optimized ateach linear velocity, to impart a mark length difference between an oddnumber length and an even number length.

In Table 14, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 14, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, T_(d1), α₁, α₁′,α_(i)=αc (i=2 to m) and α_(i)′=αc (i=2 to m−1) are constant irrespectiveof n, and T_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2 to m) andβ_(i−1)′+α_(i)′=2 (i=2 to m−1) Therefore, β_(i)=2−αc (i=2 to m−1) andβ_(i)′=2−αc (i=2 to m−2). Further, β_(m−1)′=β_(m−1)+Δ_(m−1)=βc+Δ_(m−1),α_(m)′=α_(m)+Δ_(m)=αc+Δ_(m) and β_(m)′=β_(m)+Δ_(m)′, and Δ_(m−1), Δ_(m)and Δ_(m)′ are set to be constant irrespective of m. Here, Δ_(m−1) is 0irrespective of m or the linear velocity. When n=4 to 11 (m being atleast 2), independent parameters are α₁, αc, Δ_(m), β_(m) and Δ_(m)′.

Further, when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ areset to be equal to α₁, α₁′, β_(m−1), β_(m−1), α_(m), α_(m)′, β_(m) andβ_(m)′ in the case where m=3. Accordingly, when n=4, β₂=β_(m). When n=5,β₁′=βc, α₂=αc+Δ_(m) and β₂′=β_(m)+Δ_(m)′.

Pw₀ as the writing power with which the jitter value would be minimum,is shown in Table 14. TABLE 14 -times velocity Td1 α1 αc Δm − 1 Δm βmΔm′ Pwo Pe/Pw 8 3 1.65 0.50 — — — 2.05 — 32 0.27 4˜11 1.65 0.35 0.350.00 0.25 1.15 0.75 0.27 16 3 1.30 1.15 — — — 1.30 — 32 0.27 4˜11 1.350.65 0.65 0.00 0.35 0.75 0.70 0.27 24 3 1.00 1.40 — — — 0.85 — 33 0.274˜11 1.00 1.00 0.90 0.00 0.75 0.40 0.20 0.27

FIG. 52 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 16 and 24-times velocities.

At each linear velocity, good jitter values of less than 35 nsec wereobtained with respect to mark lengths and space lengths in retrieving at1-time velocity within a range of about Pw₀±1 mW. Likewise, with respectto all mark length and space length jitters, good jitters of less than35 nsec were obtained.

Further, at each linear velocity, the modulation m₁₁ was from 60% to 80%(0.6 to 0.8), R_(top) was from 15 to 25%, and the asymmetry value was avalue within ±10%. In the vicinity of Pw₀, the desired mark lengths andspace lengths were obtained within a range of the reference clock periodT±20% with respect to any of mark lengths and space lengths of from 3Tto 11T.

In summarizing the foregoing, with the recording medium and therecording pulse division method (CD-VI-3) of the present invention, goodcharacteristics can be obtained by the recording pulse division methodhaving a small number of parameters made variable, within a wide rangeof from 8 to 24-times velocities, and the signals to be retrieved are ofa quality retrievable by a conventional CD drive. Further, also at alinear velocity between them, good characteristics can be obtained bymaking the recording pulse division method variable as in the presentinvention.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 53when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 14. In FIG. 53, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

At each linear velocity, the overwriting durability of 1000 timesrequired for CD-RW was sufficiently satisfied.

Recording Pulse Division Method CD-VI-4

This recording method is an example of the recording pulse divisionmethod (VI-B), wherein Δ_(m)′=0, and only Δ_(m−1) and Δ_(m) areoptimized to give a mark length difference between an even number lengthand an odd number length.

Specifically, overwriting was carried out at 8, 16 and 24-timesvelocities.

In Table 15, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 15, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, T_(d1)′, α₁, α₁′,α_(i)=αc (i=2 to m) and α_(i)′=αc (i=2 to m−1) are constant irrespectiveof n, and T_(d1)+α₁=T_(d1)′+α₂′=2, β_(i−1)+α_(i)=2 (i=2 to m) andβ_(i−1)′+α_(i)′=2 (i=2 to m−1) Therefore, β_(i)=2−αc (i=2 to m−1) andβ_(i)′=2−αc (i=2 to m−2). Further, β_(m−1)′=β_(m−1)+Δ_(m−1)=βc+Δ_(m−1),α_(m)′=α_(m)+Δ_(m)=αc+Δ_(m) and β_(m)′=β_(m)+Δ_(m)′, and Δ_(m−1), Δ_(m)and Δ_(m)′ are set to be constant irrespective of m. Here, Δ_(m)′ is 0irrespective of m or the linear velocity. When n=4 to 11 (m being atleast 2), independent parameters are α₁, αc, Δ_(m−1), Δ_(m) and β_(m).

Further, when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ areset to be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) andβ_(m)′ in the case where m=3. Accordingly, when n=4, β₂=β_(m). When n=5,β₁′=βc+Δ_(m−1), α₂=β_(m)and β₂′=β_(m).

Pw₀ as the writing power with which the jitter value would be minimum,is shown in Table 15. TABLE 15 -times velocity Td1 α1 αc Δm − 1 Δm βmΔm′ Pwo Pe/Pw 8 3 1.65 0.50 — — — 2.05 — 32 0.27 4˜11 1.65 0.35 0.350.75 0.25 1.15 0.00 0.27 16 3 1.30 1.15 — — — 1.30 — 32 0.27 4˜11 1.350.65 0.65 0.60 0.35 0.75 0.00 0.27 24 3 1.00 1.40 — — — 0.85 — 33 0.274˜11 1.00 1.00 0.90 0.10 0.75 0.40 0.00 0.27

FIG. 54 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 16 and 24-times velocities.

At each linear velocity, good jitter values of less than 35 nsec wereobtained with respect to mark lengths and space lengths in retrieving at1-time velocity within a range of about Pw₀±1 mW. Likewise, with respectto all mark length and space length jitters, good jitters of less than35 nsec were obtained.

Further, at each linear velocity, the modulation m₁₁ was from 60% to 80(0.6 to 0.8), R_(top) was from 15 to 25%, and the asymmetry value was avalue within ±10%. In the vicinity of Pw₀, the desired mark lengths andspace lengths were obtained within a range of the reference clock periodT±10% with respect to any of mark lengths and space lengths of from 3Tto 11T.

In summarizing the foregoing, when the recording medium and therecording pulse division method (CD-VI-4) of the present invention areapplied, good characteristics can be obtained by the recording pulsedivision method having a small number of parameters made variable,within a wide range of from 8 to 24-times velocities, and the signals tobe retrieved are of a quality retrievable by a conventional CD drive.Further, also at a linear velocity between them, good characteristicscan be obtained by making the recording pulse division method variableas in the present invention.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 55when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 15. In FIG. 55, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

At each linear velocity, the overwriting durability of 1000 timesrequired for CD-RW was sufficiently satisfied.

Recording Pulse Division Method CD-VI-5

This recording method is an example of the recording pulse divisionmethod (VI-B), wherein Δ=Δ_(m−1)=Δ_(m), and only Δ and Δ_(m)′ areoptimized to give a mark length difference between an even number lengthand an odd number length.

Specifically, overwriting was carried out at 8, 16 and 24-timesvelocities.

In Table 16, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 16, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, T_(d1)′, α₁, α₁′,α_(i)=αc (i=2 to m) and α_(i)′=αc (i=2 to m−1) are constant irrespectiveof n, and T_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2 to m) andβ_(i−1)′+α_(i)′=2 (i=2 to m−1) Therefore, β_(i)=2−αc (i=2 to m−1) andβ_(i)′=2−αc (i=2 to m−2). Further, β_(m−1)′=β_(m−1)+Δ_(m−1)=βc+Δ_(m−1),α_(m)′=α_(m)+Δ_(m)=αc+Δ_(m) and β_(m)′=β_(m)+Δ_(m)′, and Δ_(m−1), Δ_(m)and Δ_(m)′ are set to be constant irrespective of m. Here, Δ_(m−1)=Δ_(m)irrespective of m or the linear velocity. When n=4 to 11 (m being atleast 2), independent parameters are α₁, αc, Δ_(m−1)=Δ_(m), β_(m) andΔ_(m).

Further, when m=2 (n=4, 5), α₁, α₁′, β₁′, β₁, α₂, α₂′, β₂ and β₂′ areset to be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α_(m)′, β_(m) andβ_(m)′ in the case where m=3. Accordingly, when n=4, β₂=β_(m). When n=5,β₁′=βc+Δ_(m), α₂=αc+Δ_(m) and β₂′=β_(m).

Pw₀ as the writing power with which the jitter value would be minimum,is shown in Table 16. TABLE 16 -times velocity Td1 α1 αc Δm − 1 Δm βmΔm′ Pwo Pe/Pw 8 3 1.65 0.50 — — — 2.05 — 32 0.27 4˜11 1.65 0.35 0.350.25 0.25 1.15 0.55 0.27 16 3 1.30 1.15 — — — 1.30 — 32 0.27 4˜11 1.350.65 0.65 0.30 0.30 0.75 0.40 0.27 24 3 0.95 1.40 — — — 0.85 — 32 0.274˜11 .00 .00 0.90 0.40 0.40 0.40 0.00 0.27

FIG. 56 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 16 and 24-times velocities.

At each linear velocity, good jitter values of less than 35 nsec wereobtained with respect to mark lengths and space lengths in retrieving at1-time velocity within a range of about Pw₀±1 mW. Likewise, with respectto all mark length and space length jitters, good jitters of less than35 nsec were obtained.

Further, at each linear velocity, the modulation m₁₁ was from 60% to 80%(0.6 to 0.8), R_(top) was from 15 to 25%, and the asymmetry value was avalue within ±10%. In the vicinity of Pw₀, the desired mark lengths andspace lengths were obtained within a range of the reference clock periodT±20% with respect to any of mark lengths and space lengths of from 3Tto 11T.

In summarizing the foregoing, when the recording medium and therecording pulse division method (CD-VI-5) of the present invention areapplied, good characteristics can be obtained by the recording pulsedivision method having a small number of parameters made variable,within a wide range of from 8 to 24-times velocities, and the signals tobe retrieved are of a quality retrievable by a conventional CD drive.Further, also at a linear velocity between them, good characteristicscan be obtained by making the recording pulse division method variableas in the present invention.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 57when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 16. In FIG. 57, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

At each linear velocity, the overwriting durability of 1000 timesrequired for CD-RW was sufficiently satisfied.

Example 14

In the above Basic Example, two types of disks were prepared andrecording was carried out as follows.

Disk of Example 14(a)

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 15 nm of a recording layer made ofGe_(16.5)Sb₆₃Sn_(20.5)(Sn_(0.21)(Ge_(0.2)Sb_(0.8))_(0.79)), 30 nm of anupper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 3 nm of an interfaciallayer made of GeN, 200 nm of a reflective layer made ofAl_(99.5)Ta_(0.5) and about 4 μm of an ultraviolet-curable resin layer,were formed in this order to obtain a rewritable compact disk. Here, themeaning of (ZnS)₈₀(SiO₂)₂₀ indicates that it is a film obtained by highfrequency sputtering of a target having 80 mol % of ZnS and 20 mol % ofSiO₂ mixed. Further, the compositional ratio in Ge_(6.5)Sb₆₃Sn_(20.5) isan atomic ratio. The same applies in the following Examples.

The volume resistivity ρ_(v) of this Al_(99.5)Ta_(0.5) reflective layerwas about 80 nΩ·m, and the sheet resistivity ρ_(s) was about 0.4 Ω/□.

Disk of Example 14(b)

On a substrate, 82 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 15 nm of a recording layer made ofGe_(16.5)Sb₆₃Sn_(20.5)(Sn_(0.21)(Ge_(0.2)Sb_(0.8))_(0.79)), 27 nm of anupper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 3 nm of a interfaciallayer made of Ta, 200 nm of a reflective layer made of Ag and about 4 μmof an ultraviolet-curable resin layer, were formed in this order toobtain c rewritable compact disk. Here, the meaning of (ZnS)₈₀(SiO₂)₂₀indicates that it is a film obtained by high frequency sputtering of atarget having 80 mol % of ZnS and 20 mol % of SiO₂ mixed. Further, thecompositional ratio in Ge_(6.5)Sb₆₃Sn_(20.5) is an atomic ratio. Thesame applies in the following Examples.

The volume resistivity ρ_(v) of this Ag reflective layer was about 24nΩ·m, and the sheet resistivity ρ_(s) was about 0.12 Ω/□. Theinitialization of each of the disk of Example 14(a) and the disk ofExample 14(b), was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 75 μm and a minor axis of about 1.0 μm, in the minor axisdirection at a linear velocity of about 12 m/s. The irradiation powerwas about 850 mW.

On these disks, by means of the tester 2 with NA=0.50, overwriting ofEFM modulation signal was carried out at 24-times velocity by thefollowing “Recording method 1-2f” and at 8-times velocity by “Recordingmethod 2-2f”, and the characteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant at 0.27, Pw was changed, whereby theoverwriting characteristics at the respective writing powers wereevaluated. Each was evaluated by the value after overwriting ten times.Pb was set to be constant at approx. 0 mW.

This recording method is a practical usage in which the number ofparameters in the recording pulse division method (III-A) is furtherlimited.

Specifically, overwriting was carried out at 8 and 24-times velocities.

In Table 17, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and β₁′ are required, andin Table 17, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, T_(d1)′, α₁, α₁′,α_(i)=αc (i=2 to m) and α_(i)′=αc (i=2 to m−1) are constant irrespectiveof n, and T_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2 to m) andβ_(i−1)′+α_(i)′=2 (i=2 to m−1) Therefore, β_(i)=2−αc (i=2 to m−1) andβ_(i)′=2−αc (i=2 to m−2) Further, β_(m−1)′=β_(m−1)+Δ_(m−1)=βc+Δ_(m−1),α_(m)′=α_(m)+Δ_(m)=, αc+Δ_(m) and β_(m)′=β_(m)+Δ_(m)′, and Δ_(m−1),Δ_(m) and Δ_(m)′ are set to be constant irrespective of m. When n=4 to11 (m being at least 2), independent parameters are α₁, αc, Δ_(m−1),Δ_(m), β_(m) and Δ_(m)′.

Further, when m=2 (n=4, 5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ areset to be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α_(m), α₂′, β_(m) andβ_(m)′ in the case where m=3. Accordingly, when n=4, β₂=β_(m). When n=5,β₁′=βc+Δ_(m−1), α₂=αc+Δ_(m) and β₂′=β_(m)+Δ_(m)′.

Pw₀ as the wilting power with which the jitter value would be minimum isshown in Table 17. TABLE 17 Recording -times Pwo method velocity Td1 α1αc Δm − 1 Δm βm Δm′ Ex. 14-a Ex. 14-b Pe/Pw Recording 8 3 1.65 0.50 — —— 2.05 — 28 32 0.27 method 4˜11 1.65 0.35 0.35 0.25 0.15 1.15 0.55CD2-2f Recording 24 3 1.00 1.40 — — — 0.85 — 32 32 0.27 method 4˜11 1.001.00 0.90 0.35 0.50 0.40 0.00 CD1-2f

FIG. 58 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 24-times velocities. Further, FIG. 59shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8-times velocities.

FIG. 59 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8-times velocities. Further, FIG. 59shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8-times velocities.

With each of the disks of Examples 14(a) and 14(b), good jitter valuesof less than 35 nsec were obtained with respect to mark lengths andspace lengths in retrieving at 1-time velocity within a range of aboutPw₀±1 mW. Likewise, with respect to all mark length and space lengthjitters, good jitters of less than 35 nsec were obtained. However, withthe disk of Example 14(b), the range of writing power Pw in which thejitter value is low, is wider, and it can be regarded as a sample havinga wider margin for the writing power. Especially, in the data of 8-timesvelocity in FIG. 59, the difference in the power margin is distinct (seeFIGS. 59(a) and (b).)

Further, with each of the disks of Examples 14(a) and 14(b), modulationm₁₁ of from 60% to 80% (0.6 to 0.8) was obtained in a region of at leastabout Pw₀ at each linear velocity.

Furthermore, with each of the disks of Examples 14(a) and 14(b), R_(top)was from 15 to 25%, and the asymmetry value was a value within a rangeof ±10%. In the vicinity of Pw₀, the desired mark lengths and spacelengths were obtained within a range of about ±20% with respect to anyof mark lengths and space lengths of from 3T to 11T.

In summarizing the foregoing, when the recording media and “Recordingmethod CD1-2f” and “Recording method CD2-2f” of the present inventionare applied, good characteristics can be obtained by the recording pulsedivision methods having a small number of parameters made variable,within a wide range of from 8 to 24-times velocities with each of thedisks of Examples 14(a) and 14(b), and the signals to be retrieved areof a quality retrievable by a conventional CD drive. Especially, as inthe disk of Example 14(b), it is preferred to adjust the sheetresistivity of the reflective layer to be at most 0.2 Ω/□, whereby awide writing power margin can be obtained in a wide range of linearvelocities.

Example 15

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 17 nm of a recording layer made ofGe₆In₁₁Sb₆₇Sn₁₂Te₄(In_(0.11)Sn_(0.12)Te_(0.04)(Ge_(0.08)Sb_(0.92))_(0.73)),28 nm of an upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 4 nm of aninterfacial layer made of Ta, 185 nm of a reflective layer made of Agand about 4 μm of an ultraviolet-curable resin layer, were formed inthis order to obtain a rewritable compact disk. Here, the meaning of(ZnS)₈₀(SiO₂)₂₀ indicates that it is a film obtained by high frequencysputtering of a target having 80 mol % of ZnS and 20 mol % of SiO₂mixed. Further, the compositional ratio in Ge₆In₁₁Sb₆₇Sn₁₂Te₄ is anatomicity ratio. The same applies in the following Examples.

The volume resistivity ρ_(v) of this Ag reflective layer was about 27nΩ·m, and the sheet resistivity ρ_(s) was about 0.15 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 75 μm and a minor axis of about 1.0 μm, in the minor axisdirection at a linear velocity of about 16 m/s. The irradiation powerwas about 1100 mW.

On this disk, by means of the tester 2 with NA=0.50, overwriting of EFMmodified signal was carried out at 8, 16 and 32-times velocities bymeans of the recording methods as shown in Table 18, and thecharacteristics were evaluated.

The recording pulse division method at 32-times velocity is an exampleof “Recording method 1-2” and will be referred to as “Recording methodCD1-2g”. Further, the recording pulse division method at 16-timesvelocity is an example of “Recording method 2-2” and will be referred toas “Recording method CD2-2g”. Still further, the recording pulsedivision method at 8-times velocity is an example of “Recording method2-2” and will be referred to as “Recording method 2-2h”.

In Table 18, the recording method at 32-times velocity was presented asdivided into a case where n=3, 4, 5 and a case where m≦3, i.e. n is from6 to 11.

When n is 3, three parameters i.e. T_(d1)′, α₁′ and Δ₁′ are required,and in Table 18, they are presented in the columns for T_(d1), αc andβ_(m), respectively. When m=2 (n=4, 5), parameters (T_(d1), α₁, β₁, α₂,β₂) in the case of n=4 and (T_(d1)′, α₁′, β₁′, α₂′, β₂′) in the case ofn=5, are required, and they are presented in the columns for T_(d1), α₁,β₁, α_(m), and β_(m), respectively.

When m≦3 i.e. n is from 6 to 11, T_(d1)′, α₁, α₁′, α_(i)=αc (i=2 to m)and α_(i)′=αc (i=2 to m−1) are set to be constant irrespective of n, andT_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2 to m) andβ_(i−1)′+α_(i)′=2 (i=2 to m−1). Accordingly, β_(i)=2−αc (i=2 to m−1),and β_(i)′=2−αc (i=2 to m−2). Further,β_(m−1)′=β_(m−1)+Δ_(m−1)=αc+Δ_(m−1), α_(m)′=α_(m)+Δ_(m)=αc+Δ_(m) andβ_(m)′=β_(m)+Δ_(m)′, and Δ_(m−1), Δ_(m) and Δ_(m)′ are set to beconstant irrespective of m. With respect to n=6 to 11 (m being at least3), independent parameters are α₁, αc, Δ_(m−1), Δ_(m) and Δ_(m)′.

Now in Table 18, the recording method at 8 and 16-times velocity waspresented as divided into a case where n=3 and a case where n is from 4to 11. When n is 3, three parameters i.e. T_(d1)′, α₁′ and β₁′ arerequired, and in Table 18, they are presented in the columns for T_(d1),αc and β_(m), respectively. When n is from 4 to 11, T_(d1), α₁, α₁′,α_(i)=αc (i=1 to m) and α_(i)′=αc (i1=to m−1) are set to be constantirrespective of n, whereby T_(d1)+α₁=T_(d1)′+α₁′=2, β_(i−1)+α_(i)=2 (i=2to m), and β_(i−1)′+α_(i)′=2 (i=2 to m−1). Accordingly, β_(i)=2−αc (i=2to m−1), and β_(i)′=2−αc (i=2 to m−2). Further,β_(m−1)′=β_(m−1)+Δ_(m−1)=βc+Δ_(m−1), α_(m)′=α_(m)+Δ_(m)=ac+Δ_(m), andβ_(m)′=β_(m)+Δ_(m)′, where Δ_(m−1), Δ_(m) and Δ_(m)′ are set to beconstant irrespective of m. With respect to n=4 to 11 (m being at least2), independent parameters are α₁, αc, Δ_(m−1), Δ_(m), β_(m) and Δ_(m)′.

Further, when m=2 (n=4,5), α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ are setto be equal to α₁, α₁′, β_(m−1), β_(m−1)′, α₁, α_(m)′, β_(m) and β_(m)′in the case where m is 3, respectively. Accordingly, when n=4, β₂=β_(m).When n=5, β_(m−1)′=βc+Δ_(m−1), α₂=αc+Δ_(m), β₂′=β_(m)+Δ_(m)′.

Each recording method in FIG. 18 is also an example of the recordingpulse division method (VI-B) of the present invention which isapplicable to overwriting in a wide range of linear velocities, such asCAV recording.

Here, β₁′=1.38 where n=3, is different by about 4% fromβ₁′=1.19+0.25=1.44 where m=3, but this difference derives from the limitin setting pulses by an apparatus at such a high frequency, and theregularity stipulated by (VI-B) is substantially followed.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant, Pw was changed every 1 mW from about 32 mW toabout 45 mW, whereby the overwriting characteristics at the respectivewriting powers were evaluated. Each was evaluated by the value afteroverwriting ten times. Bias power Pb was set to take a constant value ofapprox. 0 mW, and Pe/Pw was set to be constant at 0.27. Pw₀ as thewriting power with which the jitter value would be minimum, is shown inTable 18. TABLE 18 Recording -times method velocity Td1 α1 β1 αc Δm − 1αm Δm βm Δm′ Pwo Pe/Pw CD2-2h 8 3 1.95 0.35 — — — — — 2.30 — 37 0.274˜11 1.80 0.20 — 0.20 0.30 0.20 0.05 1.75 0.50 CD2-2g 16 3 1.75 0.65 — —— — — 1.90 — 38 0.27 4˜11 1.60 0.40 — 0.40 0.30 0.40 0.10 1.40 0.40CD1-2g 32 n = 3 0.81 1.58 — — — — — 1.06 — 38 0.27 n = 4 0.81 1.19 1.19— — 0.81 — 0.31 — n = 5 0.81 1.19 1.38 — — 1.19 — 0.31 — m ≧ 3 0.81 1.191.19 0.81 0.25 0.81 0.38 0.31 0.00

FIG. 60 shows (a) 3T mark length jitter, (b) 3T space length jitter, (c)modulation m₁₁ and (d) R_(top) at 8, 16 and 32-times velocities. At eachlinear velocity, good jitter values of less than 35 nsec were obtainedwith respect to mark lengths and space lengths in retrieving at 1-timevelocity within a range of about Pw₀±1 mW. Likewise, with respect to allmark length and space length jitters, good jitters of less than 35 nsecwere obtained.

Further, at each linear velocity, the modulation m₁₁ was from 60% to 80%(0.6 to 0.8), R_(top) was from 15 to 25%, and the asymmetry value was avalue within ±10%. In the vicinity of Pw₀, the desired mark lengths andspace lengths were obtained within a range of the reference clock period±20% with respect to any of mark lengths and space lengths of from 3T to1T.

In summarizing the foregoing, when the recording medium of the presentinvention and the recording pulse division method (VI-B) of the presentinvention are applied, good characteristics can be obtained by therecording pulse division method having a small number of parameters madevariable, within a wide range of from 8 to 32-times velocities, and thesignals to be retrieved are of a quality retrievable by a conventionalCD drive. Further, also at a linear velocity between them, goodcharacteristics can be obtained by making the recording pulse divisionmethod variable as in the present invention.

Then, evaluation of the overwriting durability was carried out at eachlinear velocity. The overwriting cycle dependency is shown in FIG. 61when overwriting was carried out at each linear velocity at the Pw₀ andthe Pe/Pw ratio as shown in Table 18. In FIG. 61, (a) shows 3T marklength jitters, and (b) shows 3T space length jitters.

At each linear velocity, the overwriting durability of 1000 cyclesrequired for CD-RW, was sufficiently satisfied.

Further, the erase ratio at each linear velocity was measured. At8-times velocity and 32-times velocity, the 3T/11T overwriting eraseratios measured by using 3T and 11T pulses of the recording pulsedivision methods in Table 18, were at least 25 dB, respectively and thussufficient erase ratios were obtained at the respective linearvelocities.

Further, disks recorded at 32-times velocity by “Recording methodCD1-2g” in Table 18 were subjected to an accelerated test at 105° C.,whereby even upon expiration of 3 hours, no substantial deterioration ofthe recorded signals was observed. The jitter was found to have changedby about 2 nsec, and was lower than 35 nsec in retrieving at 1-timevelocity, and the reflectivity R_(top) and the modulation m₁₁ also didnot substantially decrease and maintained at least 90% of the initialvalues.

Comparative Example 1

A disk having a maximum overwritable linear velocity of about 10-timesvelocity, as disclosed in JP2001-229537, was prepared, and overwritingat 24-times velocity was tried.

On a substrate, 92 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 13 nm of a recording layer made of Ge₃In₃Sb₇₂Te₂₂(In_(0.03)Ge_(0.03)(Sb_(0.77)Te_(0.23))_(0.94)), 31 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 140 nm of a reflective layermade of an Al alloy and about 4 μm of an ultraviolet-curable resinlayer, were formed in this order to obtain a rewritable compact disk.Here, the meaning of (ZnS)₈₀(SiO₂)₂₀ indicates that it is a filmobtained by high frequency sputtering of a target having 80 mol % of ZnSand 20 mol % of SiO₂ mixed. Further, the compositional ratio inGe₃In₃Sb₇₂Te₂₂ is an atomicity ratio. The same applies in the followingExamples.

The volume resistivity ρ_(v) of this Al alloy reflective layer was 62nΩ·m, and the sheet resistivity ρ_(s) was about 0.44 Ω/□.

The initialization was carried out by scanning a laser diode beam havinga wavelength of about 810 nm and having an oval spot shape having amajor axis of about 150 μm and a minor axis of about 1.0 μm, in theminor axis direction at a linear velocity of about 7 m/s. Theirradiation power was 1650 mW.

On this disk, by means of the tester 2 with NA=0.50, overwriting of EFMmodulation signal was carried out at 24-times velocity, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant at 0.43, Pw was changed at a level of about 30mW, at which adequate signal characteristics were obtained by a singleoverwriting operation, whereby the 10-times overwriting characteristicsat the respective writing powers were evaluated. Bias power Pb was setto have a constant value of approx. zero.

As the recording method in recording at 24-times velocity, “Comparativerecording method CD1” and “Comparative recording method CD2” of Example11 were applied.

After overwriting 10 times on this disk, the 3T space length jitter wasat least 50 ns, the modulation m₁₁ was about 30% (0.3°, and R_(top) wasof a value of about 8%, and thus, at 24-times velocity, no goodrecording characteristics were obtained. The signals to be retrievedwere of a quality not retrievable by a conventional CD drive.

In the disk of this Comparative Example, first all, the Sb/Te ratio isnot more than 4.5, and the crystallization speed is slow, whereby theerasing performance is inadequate, and accordingly, overwriting isimpossible at such a high linear velocity of 24-times velocity.

Comparative Example 2

On a disk having a maximum overwritable linear velocity of about16-times velocity, and disclosed in JP2001-331936, overwriting at24-times velocity was tried.

On a substrate, 70 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 17 nm of a recording layer made ofGe₇Sb₇₈Te₁₅(Ge_(0.07)(Sb_(0.84)Te_(0.16))_(0.93)), 45 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 220 nm of a reflective layermade of an Al_(99.5)Ta_(0.5) alloy and about 4 μm of anultraviolet-curable resin layer, were formed in this order to obtain arewritable compact disk. Here, the meaning of (ZnS)₈₀(SiO₂)₂₀ indicatesthat it is a film obtained by high frequency sputtering of a targethaving 80 mol % of ZnS and 20 mol % of SiO₂ mixed. Further, thecompositional ratio in Ge₇Sb₇₈Te₁₅ is an atomicity ratio. The sameapplies in the following Examples.

The volume resistivity ρ_(v) of this Al alloy reflective layer was 100nΩ·m, and the sheet resistivity ρ_(s) was about 0.45 Ω/□.

Two disks prepared in this manner were used. The respective disks wereinitialized under the two initialization conditions.

The first initialization operation was carried out as follows. Namely, afocused laser beam having a laser wavelength of about 810 and having anoval shape with a beam major axis of about 108 μm×a beam minor axis ofabout 1.5 μm, was used and disposed so that the major axis of thisfocused beam would align in the radial direction of the disk, whereupon,while irradiating a power of from 400 to 600 mW, the disk was operatedat a linear velocity of from 3 to 6 m/s, to carry out the initializationof the disk. Further, an operation to reduce a noise of crystallizationlevel was carried out by applying servo to crystallize the groove andspaces between the grooves once with a DC light of 9.5 mW by means of atester with 780 nm and numerical aperture NA of a pickup being 0.55.

The second initialization operation was carried out as follows. Namely,a laser diode beam having a wavelength of about 810 nm and having anoval spot shape with a major axis of about 150 μm and a minor axis ofabout 1.0 μm, was used and scanned in the short axis direction at alinear velocity of about 7 m/s while irradiating a power of 1450 mW, tocarry out the initialization.

On these two disks, overwriting of EFM modulation signals was carriedout at 24-times velocity by means of the tester 2 having NA=0.50, andthe characteristics were evaluated. Here, substantially the same resultswill be obtained if NA is changed to 0.55.

As the recording method, the pulse division method as disclosed inJP-A-2001-331936 is employed. Specifically, the method of FIG. 20disclosed in JP-A-2001-331936 is employed.

JP-A-2001-331936 and the present invention are different in thedescription of the recording method. Accordingly, the recording methodwill be described hereinafter mainly along JP-A-2001-331936.

T_(d1) and T_(d1)′ are set to be constant irrespective of n.

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

α₁+β₁=2,

β_(i)+α_(i)=2 (i=2 to m−1),

β_(m)+β_(m)=1.6.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

α₁′+β₁′=2,

α_(i)′+β_(i)′=2 (i=2 to m−1),

α_(m)′+β_(m)′=2.1.

Here, α_(i)=α_(i)′=0.8 (i=2 to m−1), and β_(i)=β_(i)′=1.2 (i=2 to m−1).

When n is an even number, α₁=0.8, β₁=1.2, α_(m)=0.7 and β_(m)=0.9.

When n is an odd number, α₁′=1.0, β₁′=1.5, α_(m)′=1.0 and β_(m)′1.1.

Further, when m=2, α₁, β₁, α₂, β₂, α₁′, β₁′, α₂′and β₂′ are deemed to beα₁, β₁, α_(m), β_(m), α₁′, β₁′, α_(m)′, and β_(m)′ in the case where mis at least 3, respectively. Namely, with respect to 4T mark, α₁=0.8,β₁=1.2, α₂=0.7 and β_(m)=0.9 and

with respect to 5T mark, α₁′=1.0, β₁′=1.5, α₂ ′=1.0 and β ₂′=1.1.

When m=1, i.e. with respect to 3T mark, α₁′=1.1 and β₁′=1.5.

Even if the 10 times overwriting characteristics are evaluated by thisrecording method at 24-times velocity by setting erasing power Pe to beconstant at 10 mW and Pb to be constant at 0.8 mW and by changing Pw tocarry out overwriting at the respective writing powers, it is impossibleto obtain such good characteristics that the jitters will be less than35 nsec.

In the disks of this Comparative Example, the Sb/Te ratio is 5.2 or 5.6,while the Ge amount is as large as 7%, whereby the crystallization speedis slow, and the erasing performance is inadequate, whereby overwritingis impossible at such a high linear velocity at a level of 24-timesvelocity.

Reference Example 1

On the disk having a maximum overwritable linear velocity of about10-times velocity prepared in Comparative Example 1, overwriting of EFMmodulation signals was carried out at 10-times velocity by the following“Reference recording method CD1” as an example of the recording methodof the present invention, and the characteristics were evaluated. Such adisk itself is disclosed in JP-A-2001-229537, but there has been nodisclosure of a case wherein the recording method of the presentinvention is applied.

Using the tester 2 having NA=0.50, and while maintaining Pe/Pw i.e. theratio of erasing power Pe to writing power Pw, to be constant at 0.43,Pw was changed every mW from about 16 mW to about 24 mW, whereby theoverwriting characteristics at the respective writing powers wereevaluated. Each was evaluated by the values after overwriting 10 times.Bias power Pb was set to have a constant value of almost zero.

Reference Recording Method CD1

This recording method is a practical usage wherein the number ofindependent parameters in the recordings pulse division method (III-A)is further limited.

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.7, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m)′.

β_(m)′=β_(m)γ_(m)′.

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, α_(i)α_(i)′=αc=1 (αc is constant withrespect to i when i=2 to m−1), β_(m−1)=1, Δ_(m−1)=0.5, Δ_(m)=0.2,Δ_(mm)=0.7, α_(m)=1, β_(m)=0.4, and Δ_(m)′=0.2, and they are constantwhen m is at least 2.

However, when m=2, β₁, α₂, β₂, β₁′, α₂′ and β₂′ are deemed to beβ_(m−1), α_(m), β_(m), β_(m−1)′, α_(m)′ and β_(m)′ in the case where mis at least 3. Namely, with respect to 4T mark, β₁=1.0, α₂=1 andβ_(m)=0.4, and with respect to 5T mark, β₁′=1.5, α₂′=1.2 and Δ_(m)′=0.6.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.85, α₁′=1.6 andβ₁′=0.75.

Further, T_(d1)′, α_(i), β_(i), etc. in “Reference recording method CD1”are summarized in Table 19.

In Table 19, the recording pulse division method is presented as dividedinto a case where n=3 and a case where n is from 4 to 11. In the casewhere n=3, three parameters i.e. T_(d1)′, α₁′ and Δ₁′ are required, andin Table 19, they are presented in the columns for T_(d1), α₁ and β_(m),respectively. In the case where n is from 4 to 11, in the recordingpulse division method (III-A), T_(d1)+α₁=T_(d1)′+α₁′=2,β₁+α₂=β_(m−1)+α_(m)=2, α₁=α_(m)=αc and Δ_(m) were set to be constantirrespective of m. Therefore, although 10 parameters are presented inTable 19 including T_(d1), β₁, β_(m−1), β_(m) and α_(m), independentparameters are 5 i.e. α₁, αc, Δ_(m−1), Δ_(m) and Δ_(m)′. Further, whenn=4, β₁=β_(m−1)=βc, α₂=α_(m)=αc and β₂=β_(m). When n=5, β₁′=βc+Δ_(m−1),α₂=αc+Δ_(m), and β₂′=β_(m)′. TABLE 19 Recording method TdI α1 β1 αc βm −1 Δm − 1 αm Δm βm Δm′ Reference n = 3 0.85 1.6 0.75 recording n = 4˜11 11 1 1 1 0.5 1 0.2 0.4 0.2 method CD1

The results of evaluation of overwriting characteristics in the case of“Reference recording method CD1”, are shown in FIGS. 60.

In Figs. 62, (a) to (d) show the Pw dependency of (a) 3T mark lengthjitter, (b) 3T space length jitter, (c) modulation m₁₁ and (d) R_(top),respectively.

The optimum writing power was in the vicinity of from 16 to 23 mW, andthe overwriting characteristics were evaluated by the values at such apower.

The horizontal lines in FIGS. 62(a) and (b) indicate the standardizedupper limit value of jitter=35 (nsec) during retrieving at 1-timevelocity. Good jitter values of less than 35 nsec were obtained

From FIGS. 62(c) and (d), it is evident that the modulation m₁₁ was from60% to 80% (from 0.6 to 0.8), and R_(top) was from 15 to 25%.

Further, in the vicinity of the optimum writing power, with respect tothe mark lengths and space lengths of from 3T to 11T, desired marklengths and space lengths were obtained within a range of the referenceclock period T±10%. As the asymmetry value, a value within ±10% wasobtained.

In summarizing the foregoing, good recording characteristics wereobtained at 10-times velocity, and the retrieving signals were of aquality retrievable by conventional CD drives.

Now, the results of evaluation of overwriting durability will bedescribed in the case wherein “Reference recording method CD1” was used.The overwriting cycle dependency when repeated overwriting was carriedout at Pw/Pe=19 mW/8 mW, is shown in FIGS. 63, respectively. In FIGS.63, (a) shows 3T mark length jitter, and (b) shows 3T space lengthjitter. In FIGS. 63, for the purpose of showing the number of cycles ofrepeated overwriting on a logarithmic graph, the first recording isrepresented by first overwriting, and when overwriting was carried outnine times thereon, is represented by 10th overwriting. The overwritingdurability of 1000 cycles required for CD-RW was sufficiently satisfied.

Now, Examples in which the rewritable optical recording medium of thepresent invention and the optical recording method of the presentinvention are applied to RW-DVD.

RW-DVD Basic Example

In the following, the Basic Example of RW-DVD will be described byparticularly pointing out the differences from the Basic Example ofCD-RW.

A polycarbonate resin substrate having a thickness of 0.6 mm andprovided with a helical groove having a track pitch of 0.74 μm, a groovewidth of about 0.31 μm and a depth of about 28 nm with wobbling, wasformed by injection molding.

Each of these values of the groove shape was obtained by an opticaldiffraction method of U groove approximation using a He—Cd laser beamhaving a wavelength of 441.6 nm. To the groove wobble, addressinformation by ADIP was further imparted by phase modulation.

Recording/retrieving evaluation was carried out by means of DDU1000tester manufactured by Pulsteck Co. (wavelength: about 650 nm, NA=0.65,spot shape: a generally circular spot of 0.86 μm with an intensity of1/e², rising and falling time: less than 2 nsec., hereinafter thistester is referred to as tester 3). On the basis of the reference linearvelocity of 3.49 m/s of DVD being 1-time velocity, overwritingcharacteristics at from 6 to 10-times velocities were evaluated. Biaspower was set to be constant at 0.5 mW unless otherwise specified.

The reference clock period of data at each linear velocity was oneinversely proportionated at each linear velocity against the referenceclock period 38.2 nsec of data at 1-time velocity.

Unless otherwise specified, retrieving was carried out at 1-timevelocity. The jitter was measured by a time interval analyzer(manufactured by Yokogawa Electric Corporation) from DDU1000.

Modulation m₁₄ (=I₁₄/I_(top)) was read out by an inspection of the eyepattern on an oscilloscope.

EFM+ random data were overwritten ten times, whereupon the mark lengthsof the record data, the space lengths, the mark length and space lengthjitters, m₁₄, R_(top) and the asymmetry value were measured.

Example 16

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 70 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 12 nm of a recording layer made ofGe_(12.5)Sb_(58.3)Sn_(24.3)Te_(4.9)(Te_(0.05)Sn_(0.24)(Ge_(0.18)Sb_(0.82))_(0.71)),18 nm of an upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 2 nm of aninterfacial layer made of Ta, 150 nm of a reflective layer made of Agand about 4 μm of an ultraviolet-curable resin layer, were formed inthis order to obtain a disk.

The volume resistivity ρ_(v) of this Ag reflective is layer was 28 nΩ·m,and the sheet resistivity ρ_(s) was about 0.19 Ω/□.

The initialization was carried out by scanning a laser diode beam havinga wavelength of about 810 nm and having an oval spot shape having amajor axis of about 75 μm and a minor axis of about 1.0 μm, in the minoraxis direction at a linear velocity of about 8 m/s. The irradiationpower was 700 mW.

On this disk, by means of the tester 3 with NA=0.65, overwriting of EFM+modulation signal was carried out at 2.5 and 6-times velocities, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant at 0.29 or 0.30, Pw was changed every 1 mW fromabout 15 mW to about 20 mW, whereby the overwriting characteristics atthe respective writing powers were evaluated. Each was evaluated by thevalue after overwriting ten times.

In 6-times velocity recording, recording method DVD1-1 was applied. Inthe following, this is designated as “recording method DVD1-1a”.“Recording method DVD1-1a” is a practical usage wherein the number ofindependent parameters in the recording pulse division method (II-A) isfurther limited.

Recording Method DVD1-1a

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m−1),

β_(m−1)+α_(m)=2.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.31, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.5, provided that α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, β₁=1.25, Δ_(m−1)=0.31,α_(i)=α_(i)′=αc=0.75 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.25, Δ_(m−1)=0, Δ_(m)=0.5, Δ_(mm)=0.5, α_(m)=0.75, andβ_(m)=β_(m)′=0.5, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1, α₁=1, β₁=1.25,α₂=0.75 and β₂=0.5, and with respect to 5T mark, T_(d1)′=1, α₁′=1,β₁′=1.56, α₂′=1.25 and β_(m)′=0.5.

When m=1, i.e. with respect to 3T mark, T_(d1)′=1, α₁′=1.5 and β₁′=0.56.

On the other hand, in the case of 2.5-times velocity recording, thefollowing “Recording method DVD2-1a” was used as a specific example ofrecording method DVD2-1. “Recording method DVD2-1a” is a practical usagewherein the number of independent parameters in the recording pulsedivision method (V) is further limited.

Recording Method DVD2-1a

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m−1),

β_(m−1)+α_(m)=2.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β₁′+α₂′=2.56, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.57, provided that α_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.06, α₁=α₁′=0.94, β₁=1.44, Δ₁=0.56,α_(i)=α_(i)′=αc=0.56 (αc is constant with respect to i when i=2 to m−1),β_(m−1)=1.44, Δ_(m−1)=0, Δ_(m)=0.57, Δ_(mm)=0.57, α_(m)=0.56, andβ_(m)=β_(m)′=1.5 and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.06, α₁=0.94,β₁=1.44, α₂=0.56 and β₂=0.5, and with respect to 5T mark, T_(d1)′=1.06,α₁′=0.94, β₁′=2, α₂′=1.13 and β₂′=0.5.

With respect to 3T mark, T_(d1)′=1.06, α₁′=1 and β₁′=1.13.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 20. Each recording method is based on the recordingpulse method (II-A) or (V), and therefore, in the case where m is atleast 3, ten parameters (T_(d1), α₁, β₁, Δ₁, αc, β_(m−1), Δ_(m−1),α_(m), Δ_(m) and β_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, inthe recording pulse division method (II), are presented. However,(T_(d1)′, α₁′ and β₁′) in the case where n=3 are presented in thecolumns for T_(d1), α₁ and β₁. (T_(d1), α₁, β₁, α₂ and β₂) in the casewhere n=4 and (T_(d1)′, α₁′, β₁′, α₂′ and β₂′) in the case where n=5 arepresented in the columns for T_(d1), α₁, β₁, α_(m) and β_(m). TABLE 20Recording method T_(d1) α₁ β₁ Δ₁ αC β_(m−1) Δ_(m−1) α_(m) Δ_(m) β_(m)DVD1-1a m ≧ 3 1 1 1.25 0.31 0.75 1.25 0 0.75 0.5 0.5 n = 5 1 1 1.56 1.250.5 n = 4 1 1 1.25 0.75 0.5 n = 3 1 1.5 0.56 DVD2-1a m ≧ 3 1.06 0.941.44 0.56 0.56 1.44 0 0.56 0.57 0.5 n = 5 1.06 0.94 2 1.13 0.5 n = 41.06 0.94 1.44 0.56 0.5 n = 3 1.06 1.0 1.13

The results of evaluation of overwriting characteristics in the case of“Recording method DVD1-1a” at 6-times velocity, are shown in FIG. 64.Pe/Pw i.e. the ratio of erasing power Pe to writing power Pw was set tobe 0.30. Pw was changed every 1 mW from 15 mW to about 21 mW. Bias powerPb was constant at 0.5 mW.

In FIGS. 64, (a) to (c) show the Pw dependency of (a) jitter, (b)modulation m₁₄ and (c) R_(top), respectively.

The optimum writing power where the jitter becomes minimum, was from 18to 20 mW in “Recording method DVD1-1a”.

From FIG. 64(a), it is evident that at all Pw, the jitter duringretrieving at 1-time velocity was less than 15%. Further, the horizontalline in FIG. 64(a) indicates the jitter=10% during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, the jitter values wereless than 10%.

From FIGS. 64(b) and (c), it is evident that the modulation m₁₄ was from55% to 80% (from 0.55 to 0.8), and R_(top) was from 18 to 30%.

FIG. 65 shows the results of “Recording method DVD2-1a” at 2.5-timesvelocity. Pe/Pw i.e. the ratio of erasing power Pe to writing power Pwis made to be constant at 0.29, and Pw was changed every 1 mW from about12 mW to about 18 mW. Bias power Pb was constant at 0.5 W.

FIGS. 65(a) to (c) show the Pw dependency of (a) jitter, (b) modulationm₁₄ and (c) R_(top), respectively.

The optimum writing power is in the vicinity of from 15 to 17 mW in2.5-times velocity recording.

From FIG. 65(a), it is evident that at all Pw, the jitter duringretrieving at 1-time velocity is less than 15%. Further, the horizontalline in FIG. 65(a) indicates the jitter=10% during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, the jitter values wereless than 10%.

From FIGS. 65(b) and (c), it is evident that the modulation m₁₄ was from55% to 80% (from 0.55 to 0.8), and R_(top) was from 18 to 30%.

Further, in each case, the asymmetry was within a range of from −5 to+10%.

In summarizing the foregoing, good recording characteristics wereobtained at 2.5 and 6-times velocities, and if the recording medium andthe recording pulse division method (II-A) or (V) of the presentinvention are applied, good characteristics will be obtained also atlinear velocities between them.

Further, the erase ratio at each linear velocity was measured. The3T/14T overwriting erase ratio was measured at 2.5-times velocity byusing 3T and 14T pulses of “Recording method DVD2-1a”, and at 6-timesvelocity by using 3T and 14T pulses of “Recording method DVD1-1a”. The3T/14T overwriting erase ratios at 2.5-times velocity and 6-timesvelocity were 28 and 25 dB, respectively, and thus sufficient eraseratios were obtained at the respective linear velocities.

Further, disks recorded at 6-times velocity by “Recording methodDVD1-1a” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to be less than 10%, and thereflectivity R_(top) and the modulation M₁₄ also did not substantiallydecrease and maintained at least 90% of the initial values.

Example 17

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 13.5 nm of a recording layer made ofIn₃Ge₃Sb₈₁Te₁₃(In_(0.03)Ge_(0.03)(Sb_(0.86)Te_(0.14))_(0.94)), 20 nm ofan upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 5 m of an interfaciallayer made of Ta, 140 nm of a reflective layer made of Ag and about 4 μmof an ultraviolet-curable resin layer, were formed in this order toobtain a disk. The volume resistivity ρ_(v) of this Ag reflective layerwas 28 nΩ·m, and the sheet resistivity ρ_(s) was about 0.2 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 150 μm and a minor axis of about 1.0 μm, in the minor axisdirection at a linear velocity of about 4 m/s. The irradiation power was1200 mW.

On this disk, by means of the tester 3 with NA=0.65, overwriting of EFM+modulation signal was carried out at 2.5 and 6-times velocities, and thecharacteristics were evaluated.

While maintaining Pe/Pw i.e. the ratio of erasing power Pe to writingpower Pw, to be constant at 0.33 or 0.39, Pw was changed every 1 mW fromabout 15 mW to about 20 mW, whereby the overwriting characteristics atthe respective writing powers were evaluated. Each was evaluated by thevalue after overwriting ten times.

In 6-times velocity recording, recording method DVD1-2 was applied. Thisis designated as “recording method DVD1-2a”. This is a practical usagewherein the number of independent parameters in the recording pulsedivision method (III-A) is further limited.

Recording Method DVD1-2a

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i) in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.8125, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=0.75, α₁=α₁′=1.25, α_(i)′=αc=1.2 (αc is constantwith respect to i when i=2 to m−1), β_(m−1)=0.8, Δ_(m−1)=0.5,Δ_(m)=0.3125, Δ_(mm)=0.8125, α_(m)=1.25, and β_(m)=β_(m)′=0.125, andthey are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=0.75, α₁=1.25,β₁=0.8, α₂=1.2 and β_(m)=0.125, and with respect to 5T mark,T_(d1)′=0.75, α₁′=1.25, β_(i)′=1.1875, α₂′=1.5625 and β₂′=0.125.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.8125, α₁′=1.625 andβ₁′=0.375.

On the other hand, in the case of 2.5-times velocity recording, thefollowing “Recording method DVD2-2a” was used as a specific example ofrecording method DVD2-2. “Recording method DVD2-2a” is a practicalmethod wherein the number of independent parameters in the recordingpulse division method (VI) is further limited.

Recording Method DVD2-2a

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m).

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.875, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1.375, α₁=α₁′=0.625, α_(i)=α₁′=αc=0.625 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.375,Δ_(m−1)=0.4375, Δ_(m)=0.4375, Δ_(mm)=0.875, α_(m)=0.625, andβ_(m)=β_(m)′=0.75, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.375, α₁=0.625,β₁=1.3125, α₂=0.625 and β₂=0.75, and with respect to 5T mark,T_(d1)′=1.375, α₁′=0.625, β₁′=1.9375, α₂′=1.0 and β₂′=0.75.

With respect to 3T mark, T_(d1)′=1.4375, α₁′=1.25 and β₁′=1.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 21. Each recording method is based on the recordingpulse method (III-A), and therefore, in the case where m is at least 3,nine parameters (T_(d1), α₁, β₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m) andβ_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, in the recordingpulse division method (III), are presented. However, (T_(d1)′, α₁′ andβ₁′) in the case where n=3 are presented in the columns for T_(d1), α₁and β₁. (T_(d1), α₁, β₁, α₂ and β₂) in the case where n=4 and (T_(d1)′,α₁′, β₁′, α₂′ and β₂′) in the case where n=5 are presented in thecolumns for T_(d1), α₁, β₁, α_(m) and β_(m). TABLE 21 Recording methodT_(d1) α₁ β₁ αc β_(m−1) Δ_(m−1) α_(m) Δ_(m) β_(m) DVD1-2a m ≧ 3 0.751.25 0.8 1.2 0.8 0.5 1.2 0.3125 0.125 n = 5 0.75 1.25 1.1875 1.56250.125 n = 4 0.75 1.25 0.8 1.2 0.125 n = 3 0.8125 1.625 0.375 DVD2-2a m ≧3 1.375 0.625 1.375 0.625 1.375 0.4375 0.625 0.4375 0.75 n = 5 1.3750.625 1.9375 1.0 0.75 n = 4 1.375 0.625 1.3125 0.625 0.75 n = 3 1.43751.25 1

The results of evaluation of overwriting characteristics in the case of“Recording method DVD1-2a” at 6-times velocity, are shown in FIG. 66.Pe/Pw i.e. the ratio of erasing power Pe to writing power Pw was set tobe 0.34 in Recording method 1′. Pw was changed every 1 mW from 15 mW toabout 20 mW. Bias power Pb was constant at 0.5 mW.

In FIGS. 66, (a) to (c) show the Pw dependency of (a) jitter, (b)modulation m₁₄ and (c) R_(top), respectively.

The optimum writing power where the jitter becomes minimum, was from 17to 19 mW in “Recording method DVD1-2a”.

From FIG. 66(a),it is evident that at all Pw, the jitter duringretrieving at 1-time velocity was less than 15%. Further, the horizontalline in FIG. 66 indicates the jitter=10% during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, the jitter values wereless than 10%.

From FIGS. 66(b) and (d), it is evident that the modulation m₁₄ was from55% to 80% (from 0.55 to 0.8), and R_(top) was from 18 to 30%.

FIG. 67 shows the results of “Recording method DVD2-2a” at 2.5-timesvelocity. Pe/Pw i.e. the ratio of erasing power Pe to writing power Pwis made to be constant at 0.30, and Pw was changed every 1 mW from about15 mW to about 21 mW. Bias power Pb was constant at 0.5 W.

FIGS. 67(a) to (c) show the Pw dependency of (a) jitter, (b) modulationm₁₄ and (c) R_(top), respectively.

The optimum writing power is in the vicinity of from 17 to 20 mW in2.5-times velocity recording, and the overwriting characteristics arealso evaluated by the values at this power.

From FIG. 67(a), it is evident that at all Pw, the jitter duringretrieving at 1-time velocity is less than 15%. Further, the horizontalline in FIG. 67(a) indicates the jitter=10% during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, the jitter values wereless than 10%.

From FIGS. 67(b) and (c), it is evident that the modulation m₁₄ was from55% to 80% (from 0.55 to 0.8), and R_(top) was from 18 to 30%.

Further, in each case, the asymmetry was within a range of from −5 to+15%.

In summarizing the foregoing, good recording characteristics wereobtained at 2.5 and 6-times velocities. Further, good characteristicswill be obtained also at linear velocities between them by adjustingpulses.

Further, the erase ratio at each linear velocity was measured. The3T/14T overwriting erase ratio was measured at 2.5-times velocity byusing 3T and 14T pulses of “Recording method DVD2-2a”, and at 6-timesvelocity by using 3T and 14T pulses of “Recording method DVD1-2a”. The3T/14T overwriting erase ratios at 2.5-times velocity and 6-timesvelocity were 29 and 26 dB, respectively, and thus sufficient eraseratios were obtained at the respective linear velocities.

Further, disks recorded at 6-times velocity by “Recording methodDVD1-2a” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to have increased by 2 to 3%,but still was lower than 15% in retrieving at 1-time velocity, and thereflectivity R_(top) and the modulation m₁₄ also did not substantiallydecrease and maintained levels slightly lower than 90% of the initialvalues.

Example 18

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 78 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 12 nm of a recording layer made ofGe_(11.8)Sb_(58.8)Sn_(24.5)Te_(4.9)(Te_(0.05)Sn_(0.25)(Ge_(0.17)Sb_(0.83))_(0.70)),20 nm of an upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 2 nm of aninterfacial layer made of Ta, 200 nm of a reflective layer made of Agand about 4 μm of an ultraviolet-curable resin layer, were formed inthis order to obtain a disk. The volume resistivity ρ_(v) of this Agreflective layer was 28 nΩ·m, and the sheet resistivity ρ_(s) was about0.14 Ω/□. The initialization was carried out by scanning a laser diodebeam having a wavelength of about 810 nm and having an oval spot shapehaving a major axis of about 75 μm and a minor axis of about 1.0 μm, inthe minor axis direction at a linear velocity of about 8 m/s. Theirradiation power was 700 mW.

On this disk, by means of the tester 3 with NA=0.65, overwriting of EFM+modulation signal was carried out 10 times at 3 and 8-times velocities,and the characteristics were evaluated.

In 8-times velocity recording, recording method DVD1-2 was applied. Thisis designated as “recording method DVD1-2b”. This is a practical usagewherein the number of independent parameters in the recording pulsedivision method (III-A) is further limited.

Recording Method DVD1-2b

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.5625, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=0.875, α₁α₁′=1.125, α_(i)=α₁′=αc=0.8125 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.1875,Δ_(m−1)=0.125, Δ_(m)=0.4375, Δ_(mm)=0.5625, α_(m)=0.8125, andβ_(m)=β_(m)′=0.375, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=0.875, α₁=1.125,β₁=1.875, α₂=0.8125 and β_(m)=0.375, and with respect to 5T mark,T_(d1)′=0.875, α₁′=1.125, β₁′=1.3125, α₂′=1.25 and β₂′=0.375.

When m=1, i.e. with respect to 3T mark, T_(d1)′=0.875, α₁′=1.5625 andβ₁′=0.5.

On the other hand, in the case of 3-times velocity recording, thefollowing “Recording method DVD2-2b” was used as a specific example ofrecording method DVD2-2. “Recording method DVD2-2b” is a practical usagewherein the number of independent parameters in the recording pulsedivision method (VI) is further limited.

Recording Method DVD2-2b

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m).

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)Δ_(m).

Here, T_(d1)=T_(d1)′=1.0625, α₁=α₁′=0.9375, α_(i)=α₁′=αc=0.5625 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)=1.4375,Δ_(m−1)=0.6875, Δ_(m)=0.3125, Δ_(mm)=1, α_(m)=0.5625, andβ_(m)=β_(m)′=0.5, and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.0625, α₁=0.9375,β₁=1.4375, α₂=0.5625 and β₂=0.5, and with respect to 5T mark,T_(d1)′=1.0625, α₁′=0.9375, β₁′=2.125, α₂′=0.875 and β₂′=0.5.

With respect to 3T mark, T_(d1)′=1.0625, α₁′=1.125 and β₁′=1.

Further, T_(d1), α_(i), β_(i), etc. in each recording method aresummarized in Table 22. Each recording method is based on the recordingpulse method (III), and therefore, in the case where m is at least 3,nine parameters (T_(d1), α₁, β₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m) andβ_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, in the recordingpulse division method (III), are presented. However, (T_(d1)′, α₁′ andβ_(i)′) in the case where n=3 are presented in the columns for T_(d1),α₁ and β₁. (T_(d1), α₁′, β₁, α₂ and β₂) in the case where n=4 and(T_(d1)′, α₁′, β₁′, α₂′ and β₂′) in the case where n=5 are presented inthe columns for T_(d1), α₁, β₁, α_(m) and β_(m). TABLE 22 Recordingmethod T_(d1) α₁ β₁ αc β_(m−1) Δ_(m−1) α_(m) Δ_(m) β_(m) DVD1-2b m ≧ 30.875 1.125 1.1875 0.8125 1.1875 0.125 0.8125 0.4375 0.375 n = 5 0.8751.125 1.3125 1.25 0.375 n = 4 0.875 1.125 1.1875 0.8125 0.375 n = 30.875 1.5625 0.50 DVD2-2b m ≧ 3 1.0625 0.9375 1.4375 0.5625 1.43750.6875 0.5625 0.3125 0.5 n = 5 1.0625 0.9375 2.125 0.875 0.5 n = 41.0625 0.9375 1.4375 0.5625 0.5 n = 3 1.0625 1.125 1

The results of evaluation of overwriting characteristics in the case of“Recording method DVD1-2b” at 8-times velocity, are shown in FIGS. 68.Pe/Pw i.e. the ratio of erasing power Pe to writing power Pw was set tobe 0.24 in “Recording method DVD1-2b”. Pw was changed every 1 mW from 18mW to about 25 mW. Bias power Pb was constant at 0.5 mW.

In FIG. 68, (a) to (c) show the Pw dependency of (a) jitter, (b)modulation m₁₄ and (c) R_(top), respectively.

The optimum writing power where the jitter becomes minimum, was from 22to 25 mW in “Recording method DVD1-2b”

From FIG. 68(a), it is evident that at all Pw, the jitter duringretrieving at 1-time velocity was less than 15%. Further, the horizontalline in FIG. 68 indicates the jitter=10% during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, the jitter values wereless than 10%.

From FIGS. 68(b) and (d), it is evident that the modulation m₁₄ was from55% to 80% (from 0.55 to 0.8), and R_(top) was from 18 to 30%.

FIG. 69 shows the results of “Recording method DVD2-2b” at 3-timesvelocity. Pe/Pw i.e. the ratio of erasing power Pe to writing power Pwis made to be constant at 0.25, and Pw was changed every 1 mW from about14 mW to about 20 mW. Bias power Pb was constant at 0.5 W.

FIGS. 69(a) to (c) show the Pw dependency of (a) jitter, (b) modulationm₁₄ and (c) R_(top), respectively.

The optimum writing power is in the vicinity of from 17 to 20 mW in3-times velocity recording.

From FIG. 69(a), it is evident that at all Pw, the jitter duringretrieving at 1-time velocity is less than 15%. Further, the horizontalline in FIG. 69(a) indicates the jitter=10% during retrieving at 1-timevelocity, and in the vicinity of the optimum Pw, the jitter values wereless than 10%.

From FIGS. 69(b) and (c), it is evident that the modulation m₁₄ was from55% to 80% (from 0.55 to 0.8), and R_(top) was from 18 to 30%.

Further, in each case, the asymmetry was within a range of from −5 to+10%.

In summarizing the foregoing, good recording characteristics wereobtained at 3 and 8-times velocities, and good characteristics will beobtained also at linear velocities between them by adjusting pulses.

Further, the erase ratio at each linear velocity was measured. The3T/14T overwriting erase ratio was measured at 3-times velocity by using3T and 14T pulses of “Recording method DVD2-2b”, and at 8-times velocityby using 3T and 14T pulses of “Recording method DVD1-2b”. The 3T/14Toverwriting erase ratios at 3-times velocity and 8-times velocity were29 and 26 dB, respectively, and thus sufficient erase ratios wereobtained at the respective linear velocities.

Further, disks recorded at 8-times velocity by “Recording methodDVD1-2b” were subjected to an accelerated test at 105° C., whereby evenupon expiration of 3 hours, no substantial deterioration of the recordedsignals was observed. The jitter was found to be less than 10%, and thereflectivity R_(top) and the modulation m₁₄ also did not substantiallydecrease and maintained levels slightly lower than 90% of the initialvalues.

Example 19

In the above Basic Example, a disk was prepared and recording wascarried out as follows.

On a substrate, 80 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 13 nm of a recording layer made ofGe_(7.7)In_(10.1)Sb_(63.6)Sn_(13.8)Te_(4.8)(In_(0.1)Sn_(0.14)Te_(0.05)(Ge_(0.11)Sb_(0.89))_(0.71)),20 nm of an upper protective layer made of (ZnS)₈₀(SiO₂)₂₀, 2 nm of aninterfacial layer made of Ta, 200 nm of a reflective layer made of Agand about 4 μm of an ultraviolet-curable resin layer, were formed inthis order to obtain a disk. The volume resistivity ρ_(v) of this Agreflective layer was 28 nΩ·m, and the sheet resistivity ρ_(s) was about0.14 Ω/□. The initialization was carried out by scanning a laser diodebeam having a wavelength of about 810 nm and having an oval spot shapehaving a major axis of about 75 μm and a minor axis of about 1.0 μm inthe minor axis direction at a linear velocity of about 12 m/s. Theirradiation power was 900 mW.

On this disk, by means of the tester 3 with NA=0.65, overwriting of EFM+modified signal was carried out 10 times at 4, 10 and 12-timesvelocities, and the characteristics were evaluated.

In 10-times velocity recording, recording method DVD1-2 was applied.This is designated as “recording method DVD1-2c”. This is a practicalusage wherein the number of independent parameters in the recordingpulse division method (III-A) is further limited.

Recording Method DVD1-2c

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m)

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.47, provided that β_(m−1)′=β_(m−1)+Δ_(m−1) andα_(m)′=α_(m)+Δ_(m).

Here, T_(d1)=T_(d1)′=1, α₁=α₁′=1, α_(i)=α_(i)′=αc=0.8 (αc is constantwith respect to i when i=2 to m−1), β_(m−1)=1.2, Δ_(m−1)=0.2,Δ_(m)=0.27, Δ_(mm)=0.47, α_(m)=0.8, and β_(m)=β_(m)′=0.6, and they areconstant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1, α₁=1, β₁=1.2,α₂=0.8 and β₂=0.6, and with respect to 5T mark, T_(1d1)′=1, α₁′=1,β₁′=1.27, α₂′=1.13 and β₂′=0.6.

When m=1, i.e. with respect to 3T mark, T_(d1)′=1.2, α₁′=1.07 andβ₁′=0.8.

Further, also in the case of 12-times velocity recording, the recordingmethod DVD1-2 was applied, and this is designated as “Recording methodDVD1-2d”. This is a practical usage wherein the number of independentparameters in the recording pulse division method (III-A) is furtherlimited.

Recording Method DVD1-2d

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m).

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β_(m−1)′′+α_(i)′=2 (i=2 to m−1),

β_(m−1)′+α_(m)′=2.5, provided that β_(m−1)=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)Δ_(m).

Here, T_(d1)=T_(d1)′=0.92, α₁=α₁′=1.08, α_(i)=α_(i)′=αc=0.83 (αc isconstant with respect to i when i=2 to m−1), β_(m−1)==1.17,Δ_(m−1)=0.25, Δ_(m)=0.25, Δ_(mm)=0.5, α_(m)=0.83, and β_(m)=β_(m)′=0.75,and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.92, α₁=1.08,β₁=1.17, α₂=0.83 and β₂=0.75, and with respect to 5T mark, T_(d1)′=0.92,α₁′=1.08, β₁′=1.28, α₂′=1.14 and β₂′=0.75.

With respect to 3T mark, T_(d1)′=1.17, α₁′=1.08 and β₁′=0.67.

On the other hand, in the case of 4-times velocity recording, thefollowing “Recording method DVD2-2c” was used as a specific example ofrecording method DVD2-2. “Recording method DVD2-2c” is a practical usagewherein the number of independent parameters in the recording pulsedivision method (VI) is further limited.

Recording Method DVD2-2c

With respect to an even number mark length nT=2mT in the case where m isat least 3, at the time of recording the mark, the mark was divided intom sections, and α_(i) and β_(i) in recording pulse sections α_(i)T andoff-pulse sections β_(i)T were set to be as follows.

T_(d1)+α₁=2,

β_(i−1)+α_(i)=2 (i=2 to m).

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, at the time of recording the mark,the mark was divided into m sections, and α_(i)′ and β_(i)′ in recordingpulse sections α_(i)′T and off-pulse sections β_(i)′T were set to be asfollows.

T_(d1)′+α₁′=2,

β_(i−1)′+α_(i)′=2 (i=2 to m−1)

β_(m−1)′+α_(m)′=2.88, provided that β_(m−1)′=β_(m−1)+Δ_(m−1), andα_(m)′=α_(m)Δ_(m).

Here, T_(d1)=T_(d1)′=1.44, α₁=α₁′=0.56, α_(i)=α_(i)′=αc=0.56 (αc isconstant with respect to i when i=2 to m−1), β_(m−1) ₁=1.44,Δ_(m−1)=0.56, Δ_(m)=0.32, Δ_(mm)=0.88, α_(m)=0.56, and β_(m)=β₁=0.69,and they are constant when m is at least 3.

Further, when m=2, with respect to 4T mark, T_(d1)=1.44, α₁=0.56,β₁=1.44, α₂=0.56 and β₂=0.69, and with respect to 5T mark, T_(d1)′=1.44,α₁′=0.56, β₁′=2, α₂′=0.88 and β₂′=0.69.

With respect to 3T mark, T_(d1)′=1.44, α₁′=1.19 and β₁′=0.88.

Further, T_(d1)′, α_(i), β_(i), etc. in each recording method aresummarized in Table 23. Each recording method is based on the recordingpulse method (III), and therefore, in the case where m is at least 3,nine parameters (T_(d1), α₁, β₁, αc, β_(m−1), Δ_(m−1), α_(m), Δ_(m) andβ_(m)) and T_(d1), α_(i) and β_(i) when n=3, 4, 5, in the recordingpulse division method (III), are presented. Δ_(m)′ is set to be zero inthis Example and therefore omitted. Further, (T_(d1)′, α₁′ and β₁′) inthe case where n=3 are presented in the columns for T_(d1), α₁ and β₁.(T_(d1), α₁, β₁ and β₂) in the case where n=4 and (T_(d1)′, α₁′, β₁′,α₂′ and β₂′) in the case where n=5 are presented in the columns forT_(d1), α₁, β₁, α_(m) and β_(m). TABLE 23 Recording method T_(d1) α₁ β₁αc β_(m−1) Δ_(m−1) α_(m) Δ_(m) β_(m) DVD1-2c m ≧ 3 1 1 1.2 0.8 1.2 0.20.8 0.27 0.6 n = 5 1 1 1.27 1.13 0.6 n = 4 1 1 1.2 0.8 0.6 n = 3 1.21.07 0.8 DVD1-2d m ≧ 3 0.92 1.08 1.17 0.83 1.17 0.25 0.83 0.25 0.75 n =5 0.92 1.08 1.28 1.14 0.75 n = 4 0.92 1.08 1.17 0.83 0.75 n = 3 1.171.08 0.67 DVD2-2c m ≧ 3 1.44 0.56 1.44 0.56 1.44 0.56 0.56 0.32 0.69 n =5 1.44 0.56 2 0.88 0.69 n = 4 1.44 0.56 1.44 0.56 0.69 n = 3 1.44 1.190.88

The results of evaluation of overwriting characteristics in the case of“Recording method DVD1-2c” at 10-times velocity, are shown in FIG. 70.Pe/Pw i.e. the ratio of erasing power Pe to writing power Pw was set tobe 0.22 in “Recording method DVD1-2c”. Pw was changed every 1 mW from 22mW to about 27 mW. Bias power Pb was constant at 0.5 mW.

In FIGS. 70, (a) to (c) show the Pw dependency of (a) clock jitter, (b)modulation m₁₄ and (c) R_(top), respectively.

The optimum writing power where the jitter becomes minimum, was in thevicinity of from 24 to 26 mW in “Recording method DVD1-2c”.

From FIG. 70(a), it is evident that at all Pw, the jitter duringretrieving at 1-time velocity was less than 15%.

Further, from FIGS. 70(a), (b) and (c), it is evident that at theoptimum writing power, the clock jitter was less than 12%, themodulation m₁₄ was from 55% to 80% (0.55 to 0.8), and R_(top) was from18 to 30%.

The results of evaluation of overwriting characteristics in the case of“Recording method DVD1-2d” at 12-times velocity, are shown in FIG. 71.Pe/Pw i.e. the ratio of erasing power Pe to writing power Pw was set tobe 0.2 in “Recording method DVD1-2d”. Pw was changed every 1 mW from 23mW to about 28 mW. Bias power Pb was constant at 0.5 mW.

In FIGS. 71, (a) to (c) show the Pw dependency of (a) clock jitter, (b)modulation m₁₄ and (c) R_(top), respectively.

The optimum writing power where the jitter becomes minimum, was in thevicinity of from 26 to 27 mW in “Recording method DVD1-2d”.

From FIGS. 71(a), (b) and (c), it is evident that at the optimum writingpower, the clock jitter was less than 15%, the modulation m₁₄ was from55% to 80% (0.55 to 0.8), and R_(top) was from 18 to 30%. Further, thereason why the clock jitter at 12-times velocity exceeded 12%, is thatthe rising and falling of the recording pulses of the tester 3 used forthe measurement were slightly less than 2 nsec, which is relativelylarge as compared with the reference clock period of about 3.2 nsec. Ifthe time for the rising and falling can be shortened to a level of 1nsec, the clock jitter can be reduced to a level of 12%. The rising orfalling time at a level of 1 nsec is a value which can be sufficientlypractically accomplished at present.

The results of evaluation of overwriting characteristics in the case of“Recording method DVD2-2c”at 4-times velocity, are shown in FIG. 72.Pe/Pw i.e. the ratio of erasing power Pe to writing power Pw was set tobe 0.25, and Pw was changed every 1 mW from 14 mW to about 20 mW. Biaspower Pb was constant at 0.5 mW.

In FIGS. 72, (a) to (c) show the Pw dependency of (a) clock jitter, (b)modulation m₁₄ and (c) R_(top), respectively. The optimum writing powerwas in the vicinity of from 17 to 20 mW in 4-times velocity recording.

Further, from FIGS. 72(a), (b) and (c), it is evident that at theoptimum writing power, the clock jitter was less than 11%, themodulation m₁₄ was from 55% to 80% (0.55 to 0.8), and R_(top) was from18 to 30%.

In summarizing the foregoing, good recording characteristics wereobtained at 4, 10 and 12-times velocities. Further, good characteristicswill be obtained also at linear velocities between them by adjustingpulses.

Further, the erase ratio at each linear velocity was measured. The3T/14T overwriting erase ratios were measured by using 3T and 14T pulsesof the recording pulse division methods of Table 23, and found to be atleast 25 dB, respectively, and thus sufficient erase ratios wereobtained at the respective linear velocities.

Further, disks recorded at 10-times velocity by “Recording methodDVD1-2c” of Table 23 were subjected to an accelerated test at 105° C.,whereby even upon expiration of 3 hours, no substantial deterioration ofthe recorded signals was observed. The jitter was found to be less than12% in retrieving at 1-time velocity, and the reflectivity R_(top) andthe modulation m₁₁ also did not substantially decrease and maintained atleast 90% of the initial values.

Comparative Example 3

On RW-DVD overwritable at 4, 8-times velocity or 5-times velocity asdisclosed in Examples of JP-A-2001-331936, overwriting at 8-timesvelocity was tried.

On a substrate, 68 nm of a lower protective layer made of(ZnS)₈₀(SiO₂)₂₀, 14 nm of a recording layer made ofGe₅Sb₇₇Te₁₈(Ge_(0.05)(Sb_(0.8)Te_(0.19))_(0.95)), 25 nm of an upperprotective layer made of (ZnS)₈₀(SiO₂)₂₀, 200 nm of a reflective layermade of Al_(99.5)Ta_(0.5) and about 4 μm of an ultraviolet-curable resinlayer, were formed in this order to obtain a disk. The volumeresistivity ρ_(v) of this Al_(99.5)Ta_(0.5) reflective layer was 100nΩ·m, and the sheet resistivity ρ_(s) was about 0.5 Ω/□. Theinitialization was carried out by scanning a laser diode beam having awavelength of about 810 nm and having an oval spot shape having a majoraxis of about 108 μm and a minor axis of about 1.5 μm, in the minor axisdirection at a linear velocity of from 3 to 6 m/s. The irradiation powerwas 400 to 600 mW. Further, an operation to reduce the noise of thecrystallization level was carried out by scanning the groove with DClight of about 6 mW at 4 m/s once each by application of tracking andfocusing servo by the tester with a wavelength of 660 and NA=0.65.

On this disk, by means of the tester 3 with NA=0.65, overwriting of EFM+modulation signal was carried out at 8-times velocity, and thecharacteristics were evaluated.

As the recording method, the pulse division method disclosed inJP-A-2001-331936 is employed. Specifically, the method of FIG. 26disclosed in JP-A-2001-331936 is employed.

As the manner of description is different between JP-A-2001-331936 andthe present patent, the following description will be made primarily inaccordance with the manner of description in JP-A-2001-331936.

With respect to an even number mark length nT=2mT in the case where m isat least 3, the mark was divided into m sections, and α_(i) and β_(i) inrecording pulse sections α_(i)T and off-pulse sections β_(i)T were setto be as follows.

T_(d1)+α_(i)=2 (T_(d1)=0.95),

β_(i−1)+α_(i)=2 (i=2 to m−1),

β_(m)+α_(m)=1.4.

On the other hand, with respect to an odd number mark length nT=(2m+1)Tin the case where m is at least 3, the mark was divided into m sections,and α_(i)′ and β_(i)′ in recording pulse sections α_(i)′T and off-pulsesections β_(i)′T were set to be as follows.

T_(d1)′+α₁′=2.05 (T_(d1)′=1),

β₁′+α₂′=2.45, provided that β₁′=β₁+Δ₁,

β_(i−1)′+α_(i)′=2 (i=3 to m−1),

β_(m−1)′+α_(m)′=2.45.

Here, α_(i)=α₁′=1 (i=2 to m−1) and β_(i)=β_(i)′=1 (i=2 to m−1).

When n is an even number, α₁=1.05, β₁=1, α_(m)=1 and β_(m)=0.4.

When n is an odd number, α₁′=1.05, β₁′=1.45, α_(m)′=1 and β_(m)′=0.4.

Further, when m=2, α₁, β₁, α₂, β₂, α₁′, β₁′, α₂′ and β₂′ are deemed tobe α₁, β₁, α_(m), β_(m), α₁′, β₁′, α_(m)′ and β_(m)′ in the case where mis at least 3. Namely, with respect to 4T mark, T_(d1)=0.95, α₁=1.05,β₁=1, α₂=1 and β_(m)=0.4, and with respect to 5T mark, T_(d1)′=1,α₁′=1.05, β₁′=1.45, α₂′=1 and β₂′=0.4.

When m=1, i.e. with respect to 3T mark, T_(d1)′=1.15, α₁′=1.2 andβ₁′=0.8.

In this recording method, at 8-times velocity, Pb was set to be constantat 0.5 mW, and erasing power Pe was set to be 4 mW, 4.5 mW, 5 mW and 5.5mW. At each Pe, Pw was changed to carry out overwriting 10 times at eachwriting power to evaluate the characteristics, whereby no good resultswere obtained, as the clock jitter became at least 20%.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to obtain CD-RWcapable of one beam overwriting at a high speed of 24-times velocity or32-times velocity. Further, it is possible to obtain CD-RW which is notonly capable of 1-beam overwriting at 24-times velocity or 32-timesvelocity but also capable of overwriting at a linear velocity lower than24-times velocity.

Further, according to the present invention, it is possible to obtainRW-DVD capable of 1-beam overwriting at a high speed of 6-timesvelocity, 8-times velocity, 10-times velocity or 12-times velocity.Further, it is possible to obtain RW-DVD which is not only capable of1-beam overwriting at 6-times velocity, 8-times velocity, 10-timesvelocity or 12-times velocity, but also capable of overwriting at alinear velocity lower than 6-times velocity.

Further, according to the present invention, it is possible to obtain arecording method, whereby good recording can be carried out on arewritable optical recording medium within a wide range of from a lowlinear velocity to a high linear velocity.

The present invention has been described in detail with reference tospecific embodiments, but it should be apparent to those skilled in theart that various changes and modifications can be made without departingfrom the intention and the scope of the present invention.

Further, this application is based on a Japanese application(JP2002-34827) filed on Feb. 13, 2002, a Japanese application(JP2002-74818) filed on Mar. 18, 2002, a Japanese application(JP2002-126491) filed on Apr. 26, 2002, a Japanese application(JP2002-317858) filed on Oct. 31, 2002, and a Japanese application(JP2002-344557) filed on Nov. 27, 2002, and their entireties are herebyincluded by reference.

1. A recording method for a rewritable optical recording medium, whichcomprises: recording information on a rewritable optical recordingmedium by a plurality of record mark lengths and space lengths betweenrecord marks based on runlength limited (RLL) non-return-to-zeroinverted (NRZI) modulation system; irradiating, between record marks, alaser beam having an erasing power Pe capable of crystallizing anamorphous phase to form spaces between record marks; when a time lengthof one record mark is represented by nT (where T is a reference clockperiod), for a record mark of n=2m (where m is an integer of at least1), a time length (n−j)T (where j is a real number from −2.0 to 2.0) ofthe n=2m record mark is divided into m sections of α_(i)T and β_(i)Tcomprising α₁T, β₁T, α₂T, β₂T, . . . , α_(m)T and β_(m)T (provided thatΣ_(i)(α_(i)+β_(i))=n−j), and for a record mark of n=2m+1 (where m is aninteger of at least 1), a time length (n−k)T (where k is a real numberfrom −2.0 to 2.0) of the n=2m+1 record mark is divided into m sectionsof α_(i)′T and β_(i)′T comprising α₁′T, β₁′T, α₂′T, β₂′T, . . . ,α_(m)′T and β_(m)′T (provided that Σ_(i)(α_(i)′+β_(i)′)=n−k), applying alaser beam having a constant writing power Pw sufficient to melt arecording layer within a time of α_(i)T and α_(i)′T (where i is aninteger from 1 to m); applying a laser beam having a bias power Pbwithin a time of β_(i)T and β_(i)′T (where i is an integer from 1 to m);and further, when m≧3, for a record mark of n=2m, when a start time foran nT mark is represented by T₀, (i) generating α₁T after a delay timeT_(d1)T from T₀, then, (ii) alternately generating within i=2 to m,β_(i−1)T and α_(i)T in this order, while β_(i−1)+α_(i) is between 1.8and 2.2 (provided that at i=2 and/or i=m, β_(i−1)+α_(i) may be deviatedfrom about 2 within a range of ±0.5, and when m≧4, β_(i−1) and α_(i)take constant values βc and αc, respectively, within i=3 to m−1), andthen, (iii) generating β_(m)T, and for a record mark of n=2m+1, when astart time for an nT mark is represented by T₀, (i) generating α₁′Tafter a delay time T_(d1)′T from T₀, then, (ii) alternately generatingwithin i=2 to m, β_(i−1)′T and α_(i)′T in this order, whileβ_(i−1)′+α_(i)′ is between 1.8 and 2.2 (provided that at i=2 and/or i=m,β_(i−1)′+α_(i)′ may be deviated from about 2 within a range of ±2, andwhen m≧4, β_(i−1)′ and α_(i)′ take constant values βc and αc,respectively, within i=3 to m−1), and then, (iii) generating β_(m)′T,and with the same m, for a record mark of n=2m and a record mark ofn=2m+1, T_(d1)=T_(d1)′, α₁=α₁′, β₁=β₁′ and α_(m)≠α_(m)′, and at leastone set selected from (β_(m−1) and β_(m−1)′) and (β_(m)and β_(m)′) takesdifferent values.
 2. The recording method according to claim 1, whereinwhen m is at least 3, with the same division number m,β_(m−1)′+α_(m)′+β_(m)′ in the case where n is an odd number, is largerby from 0.5 to 1.5 than β_(m−1)+α_(m)+β_(m) in the case where n is aneven number.
 3. The recording method according to claim 1, wherein whenm is at least 3, the relations of T_(d1)′=T_(d1), α₁′=α₁, β₁+α₂=1.5 to2.5, β_(m−1)+α_(m)=1.5 to 2.5, β_(m−1)′=β_(m−1)+Δ_(m−1) (where Δ_(m−1)=0to 1), α_(m)′=α_(m)+Δ_(m) (where 0<Δ_(m)≦1), β_(m)′=β_(m)+Δ_(m)′ (whereΔ_(m)′=0 to 1) and Δ_(m−1)+Δ_(m)+Δ_(m)′=0.5 to 1.5 are satisfied, andfurther, T_(d1), α₁, β₁, αc, β_(m−1), Δ_(m−1), α_(m), β_(m) and Δ_(m)′are constant irrespective of m, and Δ_(m) takes either value of Δ_(m1)or Δ_(m2) depending upon m.
 4. The recording method according to claim1, wherein when m is at least 3, Δ_(m)=Δ_(m1)=Δ_(m2).
 5. The recordingmethod according to claim 1, wherein when m is at least 3, at least oneformula is satisfied among T_(d1)+α₁=2, α₁=αc, β₁+α₂=2, β_(m−1)+α_(m)=2and α_(m)=αc.
 6. The recording method according to claim 3, wherein whenm is at least 3, with the same division number m, the relations ofT_(d1)′=T_(d1), α₁=α₁′, T_(d1)+α₁=2, β_(m−1)′=β_(m−1)+Δ_(m−1) (whereΔ_(m−1)=0 to 1), α_(m)′=αc+Δ_(m) (where 0<Δ_(m)≦1),Δ_(m−1)+Δ_(m)+Δ_(m)′=0.5 to 1.5, β_(m)′=β_(m)+Δ_(m)′ and Δ_(m)′=0 to 1,are satisfied, and α₁, αc, Δ_(m−1), Δ_(m), β_(m) and Δ_(m)′ are constantirrespective of m, when m=2, α₁, α₁′, β₁, β₁′, α₂, α₂′, β₂ and β₂′ aremade to be equal to α₁, α₁′, β₂ (=βC), β₂′(=βc+Δ_(m−1)), α₃(=αc),α₃′(=αc+Δ_(m)), β₃ and β₃′(=β₃+Δ_(m)′) in the case where m is at least3, respectively.
 7. The recording method according to claim 1, whereinα₁′ where n=3, is larger than α₁′ where n is at least
 4. 8. Therecording method according to claim 1, wherein when T_(d1)′ where n=3and 5 is represented by T_(d1a) and T_(d1c), respectively, T_(d1) wheren=4 is represented by T_(d1b), and T_(d1) and T_(d1)′ where n is atleast 6 are represented by T_(d1d), at least one selected from T_(d1a),T_(d1b) and T_(d1c) takes a value different from T_(d1d).
 9. Therecording method according to claim 1, wherein the rewritable opticalrecording medium is a circular disk, and recording is carried out at aplurality of recording linear velocities while controlling the recordinglinear density to be constant so that it will be the same as in a diskCLV-recorded at 1-time reference velocity (i.e. 1.2 m/s to 1.4 m/s inthe case of CD, and 3.49 m/s in the case of DVD), in the same diskplane, wherein the maximum linear velocity V_(max) among the recordinglinear velocities is 20-times velocity, 24-times velocity or 32-timesvelocity in the case of CD, and 6-times velocity, 8-times velocity,10-times velocity or 12-times velocity in the case of DVD; andα_(i)=α_(imax) (where i=1 to m) at the V_(max) is from 0.5 to 2, andα_(i)′=α_(imax)′ (where i=1 to m) at the V_(max) is from 0.5 to 2, andα_(i) and α_(i)′ (where i=1 to m) are permitted to simply decrease asthe linear velocity lowers.
 10. The recording method according to claim9, wherein when the minimum linear velocity V_(min) is 8-times velocity,10-times velocity, 12-times velocity or 16-times velocity in the case ofCD, and 2.5-times velocity, 3-times velocity, 4-times velocity or5-times velocity in the case of DVD, T_(d1)+α₁, T_(d1)′+α₁′,β_(i−1)+α_(i)=2, and β_(i−1)′+α_(i)′=2 (where i=3 to m−1) are,respectively, constant irrespective of the linear velocity within alinear velocity range of from the V_(min) to the V_(max) when m is atleast
 3. 11. The recording method according to claim 9, wherein at anylinear velocity to be used, β_(m)=0 to 2, and β_(m)′=0 to 3, and β_(m)and β_(m)′ are permitted to simply increase as the linear velocitylowers.
 12. The recording method according to claim 9, wherein Δ_(m)′ ispermitted to simply increase as the linear velocity lowers.
 13. Therecording method according to claim 9, wherein among T_(d1)′, α₁′ andβ₁′ where n=3, T_(d1)′ and β₁′ are permitted to simply increase as thelinear velocity lowers, and α₁′ is permitted to simply decrease as thelinear velocity lowers.
 14. The recording method according to claim 9,wherein at any linear velocity to be used, β_(i)T (where i=1 to m) andβ_(i)′T (where i=1 to m−1) are at least 2 nsec.
 15. The recording methodaccording to claim 9, wherein when modified information is recorded onthe circular disk rewritable optical recording medium by a plurality ofmark lengths, the optical recording medium is rotated so that the linearvelocity at the outermost periphery of the record area of the opticalrecording medium, would be at least 20-times velocity, based on thereference linear velocity (1-time velocity) being a linear velocity offrom 1.2 m/s to 1.4 m/s.
 16. The recording method according to claim 15,wherein the disk is rotated so that the linear velocity at the innermostperiphery of the record area would be at least 16-times velocity of thereference linear velocity, and the recording linear velocity becomeshigher towards the outer periphery.
 17. The recording method accordingto claim 15, wherein the record area is divided into a plurality ofimaginary zones in every certain radius, and β_(m)=0 to 3, and further,β_(m) is made to simply increase towards the inner peripheral zone, andα_(i) and α_(i)′ are made to simply decrease towards the innerperipheral zone.
 18. The recording method according to claim 15, whereinthe values of Pb, Pw and Pe/Pw are substantially constant at any radialposition.
 19. The recording method according to claim 9, wherein whenmodified information is recorded on the circular disk rewritable opticalrecording medium by a plurality of mark lengths, the optical recordingmedium is rotated so that the linear velocity at the outermost peripheryof the record region of the optical recording medium, would be at least6-times velocity, based on the reference linear velocity (1-timevelocity) being a linear velocity of 3.49 m/s.
 20. The recording methodaccording to claim 19, wherein the disk is rotated so that the linearvelocity at the innermost periphery of the record region would be atleast 6-times velocity of the reference linear velocity, and therecording linear velocity becomes higher towards the outer periphery.21. The recording method according to claim 19, wherein the recordregion is divided into a plurality of imaginary zones in every certainradius, and β_(m)=0 to 3, and further, β_(m) is made to simply increasetowards the inner peripheral zone, and α_(i) and α_(i)′ are made tosimply decrease towards the inner peripheral zone.
 22. The recordingmethod according to claim 19, wherein the values of Pb, Pw and Pe/Pw aresubstantially constant at any radial position.